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Fenite and syenite are present in the margins of my study area (ultramafic-alkaline-carbonatite complex). If fenitization takes place along fractures and are relatively thick, then how can I differentiate it from syenitic intrusions? Without geochemistry, can someone suggest the differences from field and petrography. Thank you.
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We can view fenitization is a type of contact metasomatism. The fenite may vary with host rock (syenite or ultramafics) and distribution of carbonatite within them. The fenitizing fluid composition will vary with the type and composition of the intruded carbonatite. Sodic fenite and potassic fenite are commonly associated with syenite. The sodic fenite develops 'albitite' along the contact zone and may be controlled by the fracture system present. Pre-existing potash feldspar is altered to massive albitite. Potassic fenite develops 'ultrapotassic' feldspar. This may be confirmed by variation in petrography from syenite to the suspected fenite zone (and carbonatite). If the fenitization is pervasive, massive and thick, it is possible to distinguish the original and altered minerals at the outcrop. Otherwise we may need geochemical confirmation. Accessory minerals such as pyroxene in the syenite, may be altered to blue riebeckite (asbestiform), following desilication reactions, the silica generated will possess riebeckite needles as inclusions and will be noticed as greyish blue to dark blue (quartz) pebbles (Samalpatti alkaline complex). Pyroxene may be altered to green epidote or dark to greenish black biotite or vermiculite (with or without apatite) , and may be distributed as streaks in the fenite zone. Carbonatite related minerals such as monazite, apatite, corundum may occur in the fenitized zone.
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Below you can see a picture of a sandstone from the lower Buntsandstein group in Thuringia (Germany). The grey dots are sandstone, too. They are free of carbonates.
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Your "round gray parts" are reduction spheroids!
May I recommend the definition of "reduction spheroids" by
  • Beda A. Hofmann
  • Earth Science Department Natural History Museum BernBernSwitzerland
Reference work entry
Quotation:
"Reduction spheroids are small-scale (diameter: few millimeters to maximum about 20 cm) spheroidal bleached features in red-bed sediments characterized by the absence of hematite and often containing a mineralized core (center, Figure 1). Reduction spheroids result from local chemical reduction of ferric iron and other elements. Host rocks are marine and continental red beds and, more rarely, altered, hematite-stained crystalline rocks. Reduction spheroids have been described from many occurrences in red beds of widely variable age worldwide..."
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I am working on the Triassic period and particularly sedimentology, petrography, porosity, fracture and Diagenesis.
who worked at this period and has related paper.
I appreciate it.
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You may have a look at the website "Triassic Stratigraphy"
or "The European Keuper: Stratigraphy and Facies"
Best regards
K.-P. Kelber
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I am doing description of the Triassic carbonate description in terms of Diagenesis and facies analysis. where can I find the related paper or book? thanks for your recommendation
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May I recommend the following book: ISBN: 978-3-642-68423-4
Microfacies Analysis of Limestones
Author: Erik Flügel (1982)
Institut für Paläontologie Universität Erlangen-Nürnberg, Erlangen, Germany
Abstract
With the aid of sedimentological as well as paleoecological data, the microfacies types of limestone of various ages can be combined into major types which reflect the depositional and ecological conditions in a certain sedimentary environment. This concept, which was developed on Upper Triassic reef carbonates in the Alpine Mediterranean region (E. Flügel, 1972), was expanded by Wilson (1975) and made more specific for numerous Paleozoic and Mesozoic examples. These Standard Microfacies Types (SMF Types) should, however, not be overrated, although they often prove useful as a basis for discussing depositional environments.
Keywords
Patch Reef Planktonic Foraminifera Microfacies Type Facies Belt Facies Zone
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Hi all,
I'm dealing with ultrapotassic rocks from the Roman Magmatic Province (Central Italy), and I stumbled on such a phenocryst (the euhedral grey one). Zonations are clearly visible, but interference colours and habit confuses me a bit..may anyone help me out?
Is it a cpx or what? if yes, diopside?
Thanks!
Francesco
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Why is there some speculation sparked on the type of pyroxene when the angle of extinction already points to augite-pigeonite ? Yes the C axis is parallel to the thin section plane (angle of extinction in the range 40° t0 45° ( Z vs. c))
The birefrigence is rather pronounced and changes regularly according to the sections cutting the indicatrix and the crystallographic system. There is only one question still not raised and answered. What is the optical character like, positive or negative? Feldspar shows twinning lamellae following different laws, e.g. albite law. Only in metamorphic rock such twins are missing quite often.
HGD
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Hello, i have a sandstone in thin section with 15% matrix from marine deposition and i am confused with this mineral appearance in xpl it has gold colour and in ppl it has brownish yellowish colour but i can't identified it's name. I think it's calcite or lamonite but i doubt it. If you know it please help me
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Primarily, it is likely to be an Fe-bearing calcite or Fe-bearing dolomite which under the influence of oxygen has been altered as to the valence state of Fe. Since trivalent Fe cannot be accommodated into the lattice of carbonate minerals it is expelled from the structure and concentrated as a mixture of Fe oxide hydrates which suitably are denominated as "limonite" (rareky pure goethite). You are on the right track with your assumption.
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Hello,
If anyone could give an insight into what these things could be, that would be greatly appreciated. Observed under a reflected light microscope. Non-polarized light. Ordovician-Silurian Graptolithic black shale.
Thank you very much!
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Dear Mr. Saparin,
I investigated graptolite shales of Silurian and Lower Devonian age.
The only way to come to a sound conclusion is the use reflectance measurements. Metamoprhic bitumens from epi- to kataimpsonite have different reflectivity values R’min- max %). This is also true for graphite and semigraphite.
Metamorphic bitumen:
5.2 to 8.8 kata-impsonite
2.0 to 2.5 meso-impsonite
1.5 to 1.9 epi-impsonite
Semigraphite:
Structure zone 6.84 to 6.86
Wall rock alteration 6.46 to 6.55
Graphite:
0.42 -7.60 to 0.30 - 9.5
I have to rub some salt into the wound. A precise differentiation between semigraphite and graphite can only be achieved by RAMAN and spectrocopic measurements.
DILL, H.G., KUS J., GOLDMANN S., SUÁREZ-RUIZ  I., NEUMANN T., and KAUFHOLD S. (2019) The physical-chemical regime of a sulfide-bearing semi-graphite mineral assemblage in metabasic rocks (SE Germany) – A multidisciplinary study of the missing link between impsonite and graphite. International Journal of Coal Geology 214:
Can you provide me with diagenetic or metamorphic data. Is the graptolite shale overcooked ? Based upon that data cannot determine what it is but constrain the PT regime and you get an idea of the carbon modifications.
I suspect of conducting a maturity study whether the black shales are oil-, gas-prone or barren as source rocks
DILL, H.G. (1986) Metallogenesis of the Early Paleozoic Graptolite Shales from the Graefenthal Horst (Germany). - Economic Geology, 81: 889-903.
DILL, H.G. and NIELSEN, H. (1986) Carbon-sulphur-iron-variations and sulphur isotope patterns of Silurian Graptolite Shales (Germany). - Sedimentology, 33: 745-755.
DILL, H.G. and PÖLLMANN, H. (2002) Chemical composition and mineral matter of paralic and limnic coal types of lignite through anthracite rank. Upper Carboniferous coal in comparison with Mesozoic and Cenozoic coals (Germany).- Canadian Society of Petroleum Geologists  Memoir, 19: 851-867.
All publications are available on the Researchgate Server on request.
If you want to get closer to coal petrography see the textbook of:
Taylor, G.H., Teichmüller, M., Davis, A., Diessel, C.F.K., Littke, R., Robert, P., 1998. Organic Petrology. Gebrüder Borntraeger, Berlin-Stuttgart, 704 pp.
There you might find some more pictures which help you come closer to a solution.
H.G.Dill
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Feisic tuffaceous rocks of Malani Igneous Suite are generally considered to be air-borne, however, water-borne tuffs are reported from a few places. I need to understand the differences between them such as presence/absence of any structure, chemical dissimilarities etc. What are the differences between them in terms of field observations, petrography and geochemistry?
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Archi, you are correctly identified all the volcanic tuffs deposited in aqueous conditions. and described in the paper.
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I usually face the problem to distinguish between the dolomite and ankerite during the evaluation on powder XRD. Both of these minerals are found within the carbonate sedimentary rocks and belong to rhombohedral division of the hexagonal crystal system. So far having same crystal system, the XRD patterns overlap to each other and it is very difficult to distinguish that which one of these or both of these are present in a sample. Though, at some extent the chemical analysis helps due to the presence of iron in the crystal structure of ankerite Ca(FeMg)(CO3)2 and it is absent in dolomite CaMg(CO3)2. But again it is not the solution because it is also a common phenomenon that the ferrous variety of dolomite exists and there is possibility that the iron that is found in the chemical analysis could be of that variety of dolomite instead of ankerite.
Though, on the basis of petrography, the etching and staining tests are helpful but my concern is the PXRD.
Therefore, I want to know that how do we can differentiate between these two minerals on the basis of PXRD?
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Yes, as Dalibor wrote, the identification of rhombohedral carbonates from the dolomite-ankerite series by XRPD is really very difficult. There is a continuous transition between dolomite-ankerite depending on Fe/Mg ratio (apfu). The recent redefinition of the name means the majority of old specimens labelled "ankerite" are now considered to be ferroan dolomite, and true ankerite is quite rare.
I suggest chemical analysis by EMPA.
My best
Michele
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The order of crystal lization within a magmatic series allows us to deduce mineralogical evolution and also the initial composition of the magmatic fluid. Within plutonic rocks, this method is relatively easy where we based on the relationships between minerals. However, in pyroclastic rocks, the procedure is more complicated where minerals are broken. My question is, how can I deduce crystallization order within pyroclastic rocks?
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You got good suggestions from Guenter Grundmann and the Great Harald G. Dill.
You may also go through: DA Jerram et al., 2018. Petrogenesis of Magmatic Systems: Using Igneous Textures to Understand Magmatic Processes. Chapter 8 in: Steffi Burchardt (Ed), Volcanic and Igneous Plumbing Systems--Elsevier.
All best for 2020
Qasim
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I am a materials science (and metallurgy) student and geology enthusiast. Comparing these two subjects side by side, I have found out some interesting pattern.
Ironmaking slag has 40-45% CaO, 30-40% SiO2 , 10-15% Al2O3 , about 5% MgO and 1-2% FeO. Steelmaking slag can have 40-60% CaO, 10-25% SiO2, 2-10% MgO, 5-35% FeO and 0-25% P2O5.
Ironmaking slag can have, among many other minerals, Akermanite, Monticellite, Gehlenite ,Anorthite, Pyroxene etc, along with some spinels. In my opinion , it matches with some feldspathoids with slightly mafic character. Steelmaking slag is more close to alkaline earth mafic rocks and peridotites. It has a good amount of spinels, monticellite, merwinite, silicocarnite, periclase etc.
Answers from metallurgists and Geologists are welcome
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Dear Mr. Bhowmick,
Slags are artificial products representing Fe ore which is made up of the Fe ore mineral and a wide range of gangue from carbonate to silicate minerals (rock) and the slag-producing additives e.g. limestone. The entire process in blast furnace takes place at low pressure and high temperatures. As a consequence of that the natural analogue is a combination of rocks forming at high T and low P which is the mafic volcanic clan (different types of basalt, see e.g. the major mineraloids in slags are Fe-enriched olivine s.s.s., pyroxenoids, wuestite and native elements plus Ca-Mg components). As far as the metamorphic part is concerned the natural equivalent well presenting these conditions is the so-called sanidinite hornfels facies (contact metamorphic reactions of carbonates at low pressure and very high temperature). These processes result in the formation of monticellite, akermanite, melilite, tilleyite, spurrite , rankinite , merwinite and larnite. The pressure conditions are below 1 kbar and the temperature greater than 700°C.
Kind regards
H.G.Dill
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As it is known, sedimentary petrography operations are performed in carbonated rocks. before and after thin section.
But, Sometimes there may be differences between in the identification of hand samples taken from the field in the thin section examination prepared in the laboratory.
What should we do, or how should we take samples, to match the description of the samples taken from the field and the description of the thin section samples?
Is the view of the large surface of the hand sample an important definition for us or not?
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Dear Mr. Cevik,
there is simple recommendation I can give to you; determine everything in the field what you cannot determine in the laboratory, e.g., facial and structural architectural elements and save everything for the laboratory analyses such as the examination of thin section what you cannot determine with the hand lens or the unarmed eye. Then you become a very good geoscientists, because you are on the safe side and provided a good platform to create a model. If you have not done your work in the field properly the remaining downstream part does not deserve to be done at all. Your laboratory work cannot compensate for voids and deficiencies left after field work.
Kind regards H.G.Dill
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I am working on high-Al pelites and I need to know if all the white mica in my rocks are actually muscovite or some of them are pyrophyllite. Since I could not differentiate them during petrography, I want to understand and solve this problem with EPMA data of the white mica in my rocks. Please enlighten me how I can distinguish them with major oxide/cations derived from EPMA data.
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Mrs. Chaudhuri,
You have detailed answer from Prof H Dill. If you are sure that your mineral is either muscovite or pyrophyllite, the EPMA analysis can be readily used, because the former has lots of K2O and the latter has none or little of it. But there are possibilities of other minerals, also, as Prof Dill advised. You may have to go in greater details than simply assuming you may possibly be dealing with pyrophyllite.
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To have a good measure of semi-quantitative apparent temperatures of zircon crystallization, I am aware the guidelines of Watson1983, 2006 but want to use the modified version Ferry2007 where the effect of the reduced oxides aSiO2 and aTiO2 are important to be catered for. However, my petrography did not indicate presence of rutile or other Ti-rich phase like sphene but the normative Tn content is high and I noticed that where Tn s 0, there will be will be normative rutile and vice versa.
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calculating a normative mineral phase is generally not the same as using an observed mineral phase as a proxy for activity. If you don't see rutile in your crystal assemblage, then you have to assume that the rock was never saturated in TiO2 and the activity must be less than unity. The best approach would be to use MELTS to calculate the TiO2 and SiO2 activity of the melt based on the mineral assemblage observed and the composition of the rock.
Keep in mind that the zircon has to be in equilibrium with the melt when it crystallizes for this to work, even though we know that zircon can be recycled for 0.01 - 10's of Myr. Thus, if you think the zircon are anticrysts or xenocrysts, you will have to make an assumption of what the melt was at the time of crystallization.
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I think interacting magma with country rocks which have organic material or carbonate minerals is important role in precipitation Au in intrusion-related gold systems (IRGS) and Carlin-type gold deposits.
Which mechanisms are involve in trapping Au ion in magma and hydrothermal fluids?
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You could also look at these articles and the references therein: https://doi.org/10.1016/j.gca.2016.11.007 ; https://doi.org/10.1016/j.gca.2016.11.007
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Description of machines And spoftwares also
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Please read our paper on the Preparation Methods in Mineralogy and (Economic) Geology, see pdf attached. This paper includes the recommended machinery and hardware equipment, as well as small sized equipment and articles of consumption, and additional REFERENCES.
Indispensable prerequisites for the success of investigations using transmitted- or reflected-light microscopy are good thin-sections or polished-sections. As requirements of quality of microscopic mounts are just as important as those referring to the instrumentation and the optical requirements, the preparation methods for specimens from opaque minerals, rocks, milling products, ceramic materials and others are described in this paper. Contents: A) Thin- and polished sections of rocks 1. Basics for the preparation of thin sections and polished thick sections 1.1 Structure of a petrographic thin section 1.2 Selection of the object section and its three-dimensional position 1.3 "Structure" and "texture" in petrological terms 1.4 Pre-treatment of brittle specimens 1.5 Resins for embedding: Requirements 1.6 Sawing and cutting 1.7 Coarse grinding, fine grinding and lapping 1.7.1 Sample cleaning between the individual steps 1.7.2 Coarse grinding and fine grinding (I): The ‘rolling’ grinding 1.7.3 Grinding suspension: lubricants and abrasives 1.7.4 Abrasives: grain size - "mesh" and "m" 1.7.5 Lapping 1.7.6 Roughness, depth of roughness 1.7.7 Coarse grinding and fine grinding (II): The ‘cutting’ grinding 1.7.8 Fixed abrasives: hardness, texture and sharpen of grinding discs 1.7.9 Recommendations for grinding of various materials 1.8 Polishing 1.8.1 Cleaning the samples between the individual polishing steps 1.8.2 Polishing: ‘soft skin’ deformation effect, ‘Beilby-skin’ 1.8.3 Polishing suspensions: lubricants and polishing compounds, particle size and particle shape 1.8.4 Polishing discs: chemo-textiles ("KENT", “HARTFELD & Co”) 1.8.5 Polishing hardness, relief, ‘Kalbsche’ light line 1.8.6 The "REWALD –VANDERWILT” grinding and polishing method 1.8.7 Re-polishing 2a. Basic steps for producing a petrographic thin section 2b. Differences in the production of paleontological thin sections 3. Basic steps for producing a polished thin section 4. Basic steps for producing a polished thick section 5. Basic steps for producing polished hand samples and foil prints 6. Selective staining methods for thin sections, polished samples and foil prints 6.1 The distinction alkali feldspar / plagioclase (Method BAILEY, 1960) 6.2 Staining of calcite with Alizarin-Red S (Method SCHNITZER, 1958) 6.3 Staining of dolomite with p-Nitrobenzolazoresorcin (Method MANN, 1955) B) ELUTRIATION ANALYSIS OF ROCKS 1. Basics for the preparation of elutriation samples 2. Basic steps for the elutriation analysis of rocks 3. Separation methods in gravity (heavy liquid) solutions C) EQUIPMENT, HARDWARE AND SUPPLIES FOR THE PREPARATION 1. Machinery and hardware equipment 2. Small sized equipment and articles of consumption D) REFERENCES
Best regards,
Guenter Grundmann
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I need a book or paper related to concrete microscopy; exact method to identify the parameters needful for geotechnical engineering. Can anyone suggest?
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Their are several publications that are helpful but the main thing is experience. That is why ASTM C856 requires a minimum of 5 years experience under the direct supervision of an experienced petrographer. Reading something in a book alone does not prepare you for the petrographic evaluation or interpretation. Read Section 4 of ASTM C856. The other useful standards are ASTM C295 and ASTM C457. To start with, I would go to "Geomaterials Under the Microscope" by Jeremy Ingham. It is very, very basic but has color photographs and a very good section called References and Further Reading.
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Appreciate you and Professor Dr Mehrab Khan on your such efforts. Your article is just based on field relations and petrography, geochemistry will tell some more story about this article. Even Bela Ophiolite was not systematically studied. Till several questions are remaining about tectonics of Bela Ophiolites, hope in future some one of us can carry research work on the geology of Bela Ophiolite.
Thanks,
Best Wishes
Inayat Baloch
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It would give me great pleasure to see any one from my geology dept. at Baluchistan University take up further study of the Bela ophiolite. There is so much basic field mapping that needs to done first before we jump to the question of what it all means. I agree with Dr. Qasim Jan - we need "boots in the field" everywhere along this and other belts in Pakistan.
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I am looking for a commercial lab. I need to perform also stable isotopic analysis on the same samples. I am working in orogenic mesothermal veins. I will really appreciate any help
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We do also geo fluids lab atNUIG
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At this very moment (2 September; 22h00, local time), the National Museum (MN, Rio de Janeiro, Brazil), one of the most important museums of natural history in the world, is burning in flames.
In addition to the exhibitions open to the public, the MN housed some of the largest and most important scientific collections existing in Brazil. The collections of biological items included thousands of types (insects, reptiles, birds, mammals, plants, etc.).
To the taxonomists (and other colleagues): You could say how many specimens (mainly types) collected or described by you were deposited in MN? And to what taxonomic groups (family or above) these specimens belonged?
[In 2016, a coup d’état turned Brazil in a country with no future. Now, in his final months at the head of the Government, the President Michel Temer wants also to ensure that the country erase its own past.]
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I appreciate colleagues for the comments and for the suggestions.
The Brazilian press (newspapers etc.) is biased and shallow and I don’t take it too seriously. On the other hand, article published yesterday (4/9) in The Guardian had the following title: ‘Brazil National Museum: as much as 90% of collection destroyed in fire.’ At the moment, two considerations must be made: (i) this percentage should vary greatly among the different sectors of the institution (from 0% to 100% of loss); and (ii) the fact is that no one yet knows the extent of the losses.
I don’t work in the National Museum (MN) and I don’t even live in the city of Rio de Janeiro. However, a friend of mine who works at the MN sent me today (5/9) some enlightening information (especially about the biological collections), as can be read below:
(1) The so-called Imperial Palace housed most of the collections of the MN. In this building were, among others, the Department of Entomology (except part of Diptera) and part of the collections of mollusks and arachnids. Total loss: collections of insects, including several hundreds of types (e.g., about 1.300 beetle holotypes), in addition to the collections of mollusks and arachnids (but 80% of the types of mollusks have been preserved, because they were in a building annex). The departments of Geology & Paleontology and Anthropology also stayed in this main building. Total loss: the collection of Egyptian relicts (e.g., mummies) and the social anthropology library. However, some items (e.g., meteorites) are being found and collected. The building still housed an electron microscope.
(2) Outside the Palace are the following sectors: the central library; the departments of Vertebrates and of Botany; a small part of Archaeology and some laboratories of invertebrates. All are preserved.
(3) An annex to the Palace (‘Annex Alípio de Miranda Ribeiro’) was preserved. In this building are part of the the sector of dipterology and the collections of invertebrates (except mollusks and arachnids).
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Hello
I would like to know the petrography/mineralogical difference between a dolerite and tholeiite.
Does tholeiite contain olivine ONLY as phenocryst assemblage? Whereas dolerite has olivine found as both: phenocryst and groundmass? What would you call a rock that has cpx+plg devoid of olivine?
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You have very good comments from Jorge Costa-de-Moura. Only minor addition here.
1. Tholeiitic basalt can have olivine both as phenocrysts and groungmass.
2. Petrographically, if a rock essentially comprises calcic-plagioclase and clinopyroxen and content of the mafic mineral(s) is more than 40 volume percent, I would call it basalt or gabbro, depending on the grain size. If It is made up of intermediate plagioclase and clinopyroxene and also has mafic index <40, I would classify it as andesite/diorite.
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If I have a thin section with chemically reactive components (for example concrete with reactive aggregates prone to Alkali Aggregate Reaction); will I able to draw any inferences from the images taken with certain intervals of time… let us say 6 months, 1year and 2 years etc.
First of all; is that possible to make such live thin sections.
Are there any other methodologies for similar studies?
In current practice, generally these types of studies are carried out on specimens sampled at specified intervals of time or from a structure of known age.
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Dear Mohammed, sorry for the late reply, I didn't get notified that you answered. My publication is still pending (yay for the publishing process), but of course I can tell you about my samples. It all depends on the settings you use for your machine. I'm not an expert in NMR, so I can't tell you how to set this up, but I know that you can change the maximum height you can reach with the sensitive area of the MOUSE if you want to. You can do such measurements on any material that contains water (especially cement). I used it to monitor samples set on top of the magnet/RF coil unit while they were hydrating. I only did CMPG measurements at set time intervals of one hour and then one day. If you have a piece of concrete that's in a controlled environment, you can do measurements every two weeks or so, at a specific depth or several depths, then compare the resulting curves or do more complex fitting of the data. I don't know how friendly you are with NMR methods, maybe ask around your university for people who do low-field NMR and might explain more.
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I believe the mineral inside is augite though i'm not sure.
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I agree with Harald that remote idntification of minerals from photographs should be approached with a great deal of caution. May I suggest that the large rounded feature that dominates the image is an amygdale from which most of the mineral(s) filling the amygdale have been "plucked" out when the thin section was made. This is common, especially if the amygdale mineral is relatively soft. So most of what we see is a void with remnants of the filling mineral around the edges. To me its relief is far too low and the birefringence is a little low (assuming 30 micron thin section thickness), to be augite. It also appears to lack obvious cleavage. Augite is not usually a vesicle-filling mineral.
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We need for modern microscopes modern planimetry tool like it was Eltinor 4 for German Carl Zeiss Jena microscope Amplival etc.
German company Zeiss manufactured for petrographers valuable tool: Eltinor 4 – the electrical integrating point counter device, using for planimetry analyses in thin sections. Do anybody knows if is there some company producing something like it nowadays?
Any info in this matter will be welcome.
Thank you in advance.
Milan
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You can also try searching for Swift Model F, Petrog from http://www.cpx-solutions.com/_rubric/index.php?r and/or the model from Pelcon.
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For example is there any way to recognize minerals (augite, plagioclase) as more sodic or calcic?
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For plagioclase there are a few determination charts, based on the extinction angle in the zone normal to (010) - the albite twin plane, as well as the cleavage plane= which function pretty well. Try fpr example this address: eps.mcgill.ca/~courses/c312/Labs/Optlab9-13.doc @ the McGill University
For clinopyroxene it's a bit more complicated because the optical properties depend on several compositional changes, the general idea is that the optical properties and the mineral assemblage offer some clues for the composition of certain phases. Sorry for the quality of typing in this box, I notice it has become very difficult to get what you type..
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Can antiperthites serve as an evidance that the peak termal conditions for charnockitic rocks were high above temperatures obtained by geothermometers such as garnet-clinopyroxene or two-pyroxenes? If so, are there any papers/diagrams on feldspar phase diagrams that can shed the light on that? For example, the quaternary two-feldspar "granite" system, which I found in Hibbard's Petrography to Petrogenesis is, for me, partly illegible - it does not contain temperature data.
In classic Granulite uncertainity paper of Frost and Chacko (1989) pyroxene exsolution lamellae, if present, are mentioned to be a record of incipient metamorphic/igneous/ temperatures. I wonder if the feldspar exsolution pairs may be treated as the same kind of tool. I will appreciate any help.
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Charnockites can be of metamorphic and primary igneous composition. The application of exchange thermometers in both types is possible but probably limited due to subsolidus exchange which is further complicated in feldspar and pyroxene systems by subsolidus exsolution requiring attempts to re-integrate compostions.
For magmatic charnockites saturation surface thermometers (Zr, P and Ti) can provide some insight into temperatures.
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All I could identify is calcite.
The surrounding rocks are limestone that has been fractured and altered (clay replacing fossils, matrix sometimes silicified). Now maybe it is not limestone anymore.
We jokingly referred to as "fish going through the narrows".
Sorry no petrography or petrology as yet.
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Dear Mr. Issigonis, this is part of a flaser-bedded limestone and the structure may be called a stylolite in the broadest sense caused by pressure solutions. The dark gray layer represents the argillic restite of the pressure solution. There are several studies dealing with this phenomenon which have been performed by Dr. Trurnit and applied to sedimentological and mineralogical processes. Kind regards H.G.Dill
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Some author proposed that there are two enriched reservoirs, with mantelic characteristics, in the continental crust. However it is not clear if these storage influence the surronding source rocks from lower crust.
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I believe that EM-I end-member is strongly influenced by the recycling of ancient lower continental crust. On the other hand, EM-II end-member is more likely associated to recycling of subducted sediments.
See attached some articles of mine dealing with this argument.
Cheers,
michele
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The carbonate outcrop comprised of alternating limestone-marl succession. The depositional environment interpreted was open lagoon. Both the elemental and C/O isotope composition indicates original mineralogy as aragonite and similar composition to the seawater rather than freshwater. High Sr (~1000-2000 ppm) and low Mn (constant ~100 ppm), C isotope ~0 to 1‰ PDB and O isotope ~-3 to -4‰ PDB. However, when observed under microscope, the texture of the fossils has been altered. The surrounding matrix is micrite. From staining method, the mineral was observed to be calcite
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Dear Nur Aisyah,
The carbon isotopic composition of a carbonate is related to the balance of the inorganic and organic sources of carbon, which control the carbon isotopic composition of the  CO2 reservoir. In organic-rich environments, bacterial processes dominate, including (1) bacterial sulfate reduction, in which reduced carbon is oxidized to CO2, occurs in the uppermost sediments where sulfate ions are available; and (2) downward, in the sulfate-free zone, methane-generating bacteria monitor the fermentation and carbonate reduction processes, both of which produce methane.
In bacterial sulfate reduction reactions 1 and 2, the produced CO2 is depleted in 13C because the carbon originates from 13C-depleted sources, organic matter ( 13C~-25 ), and methane (-100  < 13C <-40 ).
In the bacterial fermentation reaction 3, the carbon isotopic fractionation between the two by-products may reach 80  the light carbon is preferentially transferred to CH4, while the CO2 is highly enriched in 13C relative to the initial organic substrate. In the bacterial carbonate reduction reaction 4, the 12C-rich CO2 is used preferentially by bacteria to form CH4 and the residual CO2 become enriched in 13C as the reaction proceeds. Therefore, the CO2produced or remaining during methanogenesis is characterized by high  13C values.
Last but not least, the chemical and carbon isotopic compositions of the diagenetic carbonates are controlled by the CH4-CO2 input-output balance, which depends on the bacterial reduction of sulfate and of carbonate.
Regards,
Shahrokh.
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As we know coal has different qualities, so is it necessary that they would have the same adsorption capacity (particularly of methane). I think they are not but not sure!
The second problem is that if we calculate the pores volume of any coal type through petrography, can it be an actual analogue for the coal bed methane present there, which is normally find via other methods. 
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This is actually a question that cannot get answered easily or straight forward: Coal is a very heterogeneous material in terms of composition, chemistry and pore size distribution to start with and it underlies a burial history with temperature changes that can heavily affect the sorption characteristics. There is plenty of published material on this.
Basically, low rank coal sorbs quite significantly and so does high rank coal. Bituminous coal sorbs way less simply because when coal reaches oil maturation, the micropores are filled with oil droplets and are therefore not accessible to gas. This porosity cannot be seen with a standard microscope, even a TEM has difficulties making these pores of <2nm visible.
The composition of coal is determined by the depositional environment, geological age, plant input and again burial history which means that if you find two pieces of coal of the exact same age and maturity, sorption capacity can be very different, depending on the chemistry of the sorption sites. Likewise, Carboniferous and Permian coals can sorb differently, even if all other parameter are the same.
The same holds for CO2/CH4 competitive adsorption where, yes, in general CO2 sorbs more than CH4 but the ratio can vary significantly depending on coal type, coal maturity and pressure. Chemistry of sorption sites plays  role but also pore size distribution.
If you want to know more about this, please consult literature by Bernhard Krooss and Yves Gensterblum or Marc Bustin and others
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I want estimate production rates of the biogenic fraction of coastal sediments where this fraction is the dominant one
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Dear Francesco,
You may obtain some crude chronological estimate by trying the following:
A) Select the robust taxa and observe their taphonomic state (abrasion, disarticulation, fragmentation, secondary rounding, etc.).
B) Note the annual input rate (seasonally variable) of the chosen taxa and the rate of taphonomic changes with time.
C) Use data from steps A and B to infer the antiquity (very rough estimate only) of the rehash assemblage.
Best wishes
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I have age control of a formation and want to combine sequence stratigraphy and petrography of a formation. I mean I want to use petrography as an interpretation tool_________!
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No.
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In simple calcissilicated rocks, the granulitic facies would be attested by the presence of forsterite or grossular, up to fCOquantity.
Anyhow, the coexistence of Diopside and Enstatite in a quartz saturated rock, with minor retrometamophic poikiloblastic hornblende it's enough to testify a retrometamorphic path from granulite to amphibolite facies?
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Your question is in some what confused manner
are you asking or giving a statement?
As I understood you would like to know the mineral assemblage when the protolith is sedimentary either carbonate-greywacke
Granulite facies metamorphism occurs at temperatures of approximately 500 to 700 degrees celsius and pressures of 8-70 kbar.
Changes in mineralogy depends very much on protolith,
In case of pelites the mineral assemblage is - microcline +/- plagioclase +/- scapolite +/- garnet +/- cordierite (low-P) +/- andalusite (low-P) +/- kyanite (high-P) +/- sillimanite (moderate, low-P, high-T) +/- graphite +/- rutile +/- ilmenite +/- olivine +/- corundum +/- spinel +/- sapphirine (high T).
In case of quartz-feldspathic rocks the mineral assemblage is - microcline + plagioclase + garnet +/- pyroxene +/- hornblende.
whereas in case of calc-silicate rocks the mineral assemblage is- calcite, dolomite, quartz, diopside, scapolite, forsterite, wollastonite, graphite.
Small amounts of hornblende are often present, which is likely due to the water pressure being lower than lithostatic pressure during most granulite facies metamorphism.
Evidence for relatively low water pressures comes from fluid inclusion data indicating carbon dioxide-rich fluid compositions and from preservation of some bulk compositions that should have undergone nearly total melting at granulite temperatures if water pressure had been equal to lithostatic pressure.
Thus the presence of hornblende need not always indicate retrograde metamorphism, you observe it's textural association with pyroxene to ascertain the retrograde metamorphism.
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I have found two varieties of serpentinites with different colours and almost mineralogical composition.These serpentinites are closely found in the same place with different degree of serpentinization....How? 
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Serpentinite is a rock composed of one or more serpentine group minerals
Serpentinization is hydration and metamorphic transformation of ultramafic rocks, composed mainly of olivine and pyroxenes,
There are three main serpentine polymorphs—chrysotile, lizardite, and antigorite—whose stability fields are dependent on both thermodynamic and kinetic parameters
The final mineralogy depends both on rock and fluid compositions, temperature, and pressure. Antigorite forms in reactions at temperatures that can exceed 600 °C (1,112 °F) during metamorphism, and it is the serpentine group mineral stable at the highest temperatures. Lizardite and chrysotile can form at low temperatures very near the Earth's surface.
Ultimately depends on the Fe-Mg lattice diffusion in olivine temperature of serpentinization
You can refere
1. Evans, 2010, p. 879 of Geology. 
2. Serpentine and serpentinization: A link between planet formation and life in the same issue of Geology by..Othmar Müntenerin
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Recently, I analyzed REE of certain granites. The chondrite normalized REE plot shoed -ve Pr anomaly. I am puzzled to see the profile!
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A significant proportion of REE minerals reside in accessory minerals in common rocks. Praseodymium (Pr),  is a LREE which is commonly concentrated in accessory minerals of the rocks. Praseodymium is found in the rare earth minerals monazite and bastnäsite, typically comprising about 5% of the lanthanides contained therein.
as i have observed in literature pertaining to chondrite normalized patterns of some of  these common accessory minerals, it is found that mineral zircon shows negative Pr anomaly, i.e., your sample might be having a zircon concentration there by giving negative Pr anomaly or it could be depletion of Pr bearing monazite/ bastnasite in the sample Hope it is useful to some extent.
you may refer the following paper for further details.
Reference: Geochemistry of the Lanthanide Elements
Fernando Bea
Department of Mineralogy and Petrology. University of Granada
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We have some types of sandstone where we have carried out the petrographic studies along with XRD and EDS and found that in most of the samples the ratio of calcite to quartz is 30:60, 40:50, 50:40, 60:30; the remaining are the different types of clay minerals. A few grains of feldspar, rock fragments and muscovite were also observed during the thin section study but these are in traces.
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Dear Muhammad,
The answer takes one back to the question concerning the provenance of the sandstone. Since the calcite is in the form of cement, it was precipitated from solution. Sources of calcite could come from dissolution of former calcium rich minerals such as calcic plagioclase, Ca-pyroxenes, usually of igneous source, as well as carbonate sediments. Also since the framework elements are quartz in minor quantities, consider occasional transport of quartz  into a carbonate shelf, away from clastic influx, i.e. Asoori's No. 2  answer as above.
Are the quartz strained, showing undulose extinction (metamorphic) or not?, Tells if the source is from basement or older sedimentary source.  
What sedimentary structures are associated with the deposits?
All the best.
Obianuju P. Umeji
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carried out sintering experiments on kaolin sample with various temperature. Test has been done (sintering studies) on 1600 degree C temperature with various time (2-5 hours) . we got quite high recovery (sample weight) after sintering in 5 hours time period.
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Sorry, I cannot help you in this respect. I have some experience in analysing slags from the time I was working in an ironwork. For quantification of mineral composition of composite samples containing slag we used combination of chemical composition, micro-DTA, sometimes X-ray diffraction and microscopic point counter technique. Probably the X-ray Diffraction would be the best and the easiest way to get some information about the quantity. I wonder - do you have Scanning Electron Microscope? What, if you try to make some analyses there, may-be mapping, linear or simply counting grains, if they are recognisable - just for basic insight?
Best wishes & regards.
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I have made peperites in the lab using basaltic melts and wet sediments (silty sand and silts). I have 3 different textures (block, globular and ragged) but my field area contains mostly ragged textures. 
The photos would be a great help in comparing what I have done in the lab with example from nature. If you are interested, please contact me and I will provide you with my email.
Thanks
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There are a couple of good field photos and drawings on blocky and fluidal peperites in the attached JVGR paper. These are examples from the Miocene to Pliocene Bakony-Balaton Highland volcanic field in Hungary.
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We Know Nb and Ta are usually coupled in most geological processes. However, in my a recent study on a granitoid, I observe the decoupling between elements Nb and Ta. In the samples, element Nb is obviously depleted whereas Ta is variable in content from highly depleted to slightly enriched. I want to ask what geological process leads to Ta decoupled from Nb in granitoid? Fluid contamination or fractional crystallization of both major phases and accessory phases?
A spider diagram is attached here.
Thanks. With regards.
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Hi Lu Lu,
The subject is also treated in this paper:
Green, T. H. (1995) Significance of Nb/Ta as an indicator of geochemical processes in the crust-mantle system. Chemical Geology 120(3–4):347-359.
Regards,
Antoine Caté
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Dear All.
I am student with problem in thin section. Our machine in University is Thermoscientific tools. The funny case is stock for Microscopes slide which empty. 
Do you know information, where is the place for buy Menzel Glaser 50 OTG 90, 28 x 48 mm, thick 1,8-2.0 mm... It is for my thesis, i was waiting until 1 years for it and they did not buy!!!
Thanks.
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Dear Mathias H. Köster...
Thanks for your information. It will help....
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I have got 50 sediment samples taken from different sites and I want to determine heavy mineral proportions for each site
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Are you looking at the minerals in thin section or grain mount?  For what purpose are you doing this?  In my exerience, there s no statistically viable way to make such counts with the hope of comparing one sample to another.  When I work with heavies, it is often more important to understand exactly what is there rather than the proportions of the various populations.  
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soil micromorphology; petrography; archeologica soil
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Dear Daniel,
here some pictures of vivianite we observed in urban Dark Earth contexts in Brussels (Belgium):
a vivianite micro crystal from urban Dark Earth from the site of 'Rue d'Une Personne' associated to the partial decomposition of plant remains in a wet context (PPL and XPL).
and the next image viviniate formation associated to the accumulation of (human) excrements in a wet environment (site of rue des Pierres).
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Dear colleagues
The attached file consists of an image which taken from paleogene phosphatic limestones of Pabdeh Formation in Lar mountains (south west of Iran). Nominated layer belongs to middle part of this Formation and based on planktonic foraminiferal studies (Daneshian et al., 2015) estimated Lutetian-Bartonian stage. Field and petrographic studies denote that there are some sedimentary structures such as: Hummocky cross stratification, cross lamination, ripple marks and amalgamation which can be categorized as tempestites. Please, if you find any mistakes in my opinion, could you please correct them?
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HI,
Please, read this article :
Pomar L., Morsilli, M, Hallock, P. et Bádenas, B. 2012. Internal waves, an underexplored source of turbulence events in the sedimentary record. Earth-Science Reviews, 111, pp. 56-81.
It can gives you more ideas.
Good luck
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I'm doing a petrography study of granitoids and I suspect, based on optical properties, the presence of these two minerals in my thin sections. However, I don't have any certainty and I don't know how to distinguish between them since they have very similar optical properties. I would appreciate any tips.
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Dear Mr. Quelhas,
The following optical data are very diagnostic:
Xenotime (one crystallographic axis/ straight extinction) vs. monazite (two crystallographic axis/ oblique extinction)
birefringence (X : 0.095-0.100) vs. (Mo: 0.049-0.050)
In a heavy mineral mount, X often looks like a carbonate mineral displaying some kind of a "pseudo-pleochroism".
X often morphologically shows up as "squares", whereas Mo is "rhomb-shaped".
Best regards
H.G.Dill
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I am doing my PhD thesis about granitoids and I don't know which is the more appropriate way to classify a granitoid according to the IUGS classification: through modal analysis or normative analysis. Or maybe both.
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Dear Mr. Quelhas,
if you confine your study to thin sections only, then you will have no other choice to use the point counter only. This method, however, only gives reasonable results in case of coarse to medium-grained rock slaps which under the petrographic microscope allow for a good identification of minerals. In fine-grained rocks the method is very limited.
If you have a SEM/EDX or SEM/WDX at hands you may also use the cut of the rock slap under the SEM for a more advanced determination and quantification of the minerals. Combining the thin section and its "mirror image", the rock slap, under the SEM, is the most appropriate way and you should reach reasonable results.
A third step which is not an easy task for the beginner is XRD, using the Rietveld phase analysis and quantification.
If you combine these three steps you will get a good phase analysis which may help you plot your data in a ternary or double-triangular plot. And you are on the safe side of the road to success.
I wish you good luck.
H.G.Dill
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Recently I read a review paper written in Chinese in 1980s talking about composition of Calcic Amphiboles and its petrology significance.The Si-Ti-Al ternary diagram, Al-Si diagram, TiO2-Al2O3 diagram et al. are used to distinguish the amphibole derivations(Mantle one or crustal one?).
My question is these criteria is right(suitable) or not today.
Thank you very much!
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In 1980s there was no reasonable definition about the origin of amphiboles in the literature. However, three decades of geological studies have made it clear that amphibole can be generated in both crustal and mantle rocks, depending on water availability. If amphibole occurs in the crustal rocks of mafic to felsic composition, it is crustal amphibole; if it occurs in the mantle rocks of ultramafic composition such as peridotite, pyroxenite and hornblenite, it is mantle amphibole.
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What is the exploration history and structural evolution of the forth basin?
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Do the coal petrography serve this purpose? Is there any kind of possibilities of petrographic indexing for predicting the washability behavior?
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Dear Mr Mishra,
Since the distribution of coal wash fractions is primarily a function of density the basic properties of the raw coal can represent good indicators of possible washability properties and wash curves.
Other indicators include general lithological composition obtained from an understanding of depositional environment, such as whether the coal is a distinct homogeneous seam, or comprises minor coal/dirt laminations (colloquially “barcodes”). The composition of the seam can be determined through other geological techniques such as geophysical logging, which are very useful in this regard. A mid density (say 1.6 SG) homogenous seam would have a linear wash curve, with approximate equal yields per float fraction. A low density (say 1.4 SG) heterogeneous seam would likely contain a higher yields in the lower density washes, few middlings and some distinct dirt bands manifested as increased yields in the floats >2.0. Seam homogeneity can be determined by examination of density or gamma logs which may have been acquired during investigation of the deposit.
The distribution of coal mass per float fraction yield is of primary importance however the behaviour of other components of the coal are also significant. For example the Total Sulphur (%) of the raw sample illustrates the proportion of sulphur in the coal, however additional testing would be required to determine, or predict, how the sulphur behaves during washing (dense pyritic sulphur is “washed out” whereas sulphur present organically or as sulphides within the coal itself tend to remain in the less dense fractions).
Kind regards,
Sam Moorhouse
Senior Geologist, Mining UK, RHDHV
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I am supposed to estimate the viscosity of melt in a shock by lightning setting. The target rock was seeberger sandstone and the cathode that produced the shock is made out of Cu (Exact formula CuZN39Pb3 (MS58) Material Number 2.0401). Therefore the melt spherules in the following pictures are made mostly of Cu and the melt threads of SiO2.
Looking forward to your answers!
Houssam
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Thank you Florian. Your clarification is much appreciated.
Have a nice day!
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I am running a round robin test on applied petrography and I am a bit lost on one sample, for which I do not have any precision concerning origin, chemistry etc. The aggregate is black so I thought "ok this is a basalt" but I do not see any lath of plagioclase (fortunately there is olivine). I suspect some tridymite/cristobalite, volcanic glass (devitrified?) but what about the prismatic crystals (high birefringence colors) which form almost all the groundmass ? Many thanks in advance.
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I also vote for clinopyroxene. The larger laths show the expected interference colors for augite; the smaller grains have lower interference colors, consistent with thicknesses less than 30 microns. The relief and inclined extinction are also consistent with cpx.  -- Jane
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We can infer the source features and evolution of a magma during its ascent from spider plots of trace and REE elements, by normalizing the elemental content of rocks with different reservoir elemental composition. In case of granitic rocks (I-type), which have upper continental crustal-like primitive mantle normalized pattern (see attached file)  we mostly assume that either the rocks are crustal derived or mantle derived, but contaminated by crustal rocks. Can fractional crystallization of the primitive mafic magma (or andesitic; mantle derived)  give such  pattern?
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Dear Mr. Aminov,
you expect too much from a single set of trace elements normalized to a standard and overstretch the possibilities of such analyses. You have to take a more diversified approach also including REE (see first response of Dr. Towe), isotopes and last but not least carefully examine the lithology of the volcanic rock to see which processes affected this magmatic rock. It is not only the source that counts. On the way up a magma can also be contaminated.
Best regards
H.G.Dill
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During some routine pegmatite mineralogy we came across an unknown mineral in association with the very rare-mineral 'fluorcalciomicrolite'. We no longer have the grab sample from which the thin section was taken but still have the thin section and have had the opportunity to analyse it quantitatively, along with some element mapping.
The results confirm that our mineral is possibly unique or possibly a second world occurrence of the recently discovered 'peterandresenite' but with high concentrations of Ta, presumably substituting for the Nb. The question is, what additional work can be done to confirm or publish the results bearing in mind all that we have is a normal 30 micron thin section of the mineral in question? 
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Dear Dr. Brough,
the addressee is the Commission on New Minerals, Nomenclature and Classification (CNMNC) of IMA
Details for new minerals are found here:
Best regards
H.G.Dill
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Hi dears. I need your help about the petrography of this carbonate limestone. It is composed of calcite and quartz. Best regards
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Dear colleagues,
we have to live with the classification as they exist and cannot create for each and every rock sample a system of its own. Even if some classification schemes may not reach the level agreed by common consensus, Leighten & Pendexter provided a classification that can already be applied in a stage where we not exactly know what the carbonate rock has been derived from. We can observe in both images purple spots (mineral ?), there is mouldic porosity and we can identify vugs with XX of an unknown mineral. There are several questions still waiting an answer.
Best regards
H.G.Dill
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Why should we put the early marine strata unit in the foreland basin system (peripheral foreland basin)? I am wonder when a basin can be named foreland basin, before the final collision or after? If it is post-collision, what is the difference between the marine strata bearing forleand basin and the remnant oceanic basin?
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Dear Longgang,
The formation of a foreland basin starts during the continent-continent collision when one of the two continental plates starts to be subducted by the obducted plate. The continent-continent collision starts after closure of the remnant ocean. Accordingly, the foreland basin develops not before or after, but during the collison. The sedimentation into the foreland basin occurs during the rise of the newly forming mountain range. The reasons for intense sedimentation into the forelland basin are the intense erosion in the rising mountains and the increasing relief between the rising mountains and the descending foreland basin. If marin or terrestrial sedimentation occurs in the foreland basin is controlled by the relative sea-level and the tectonic conditions. If the grade of mountain rise is high, the subsidence in the foreland bain is also high and marin transgression into the foreland basin may occur if the relative sea-level is high.
The sedimentation in the closing but stll deep ocean before the collision is dominated by deep-marin deposits ("Flysch") whereas sedimentation into the foreland basin is dominated by shallow marine conditions. Characteristic for marine foreland basin deposist are shallow marine siliciclastic deposits in the basin and deltaic fan conglomerates around the rims of the basin.
All the best,
Elmar
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I am trying to find out more information about the formation of a stone from India that is used for building and is known in the stone trade as Kashmir White.  I have attached a couple of typical photos of the stone.  Normally I would hope to obtain a sample and petrographically examine it myself, but unfortunately do not have the time available to do so.
The stone appears to be a partially metamorphosed granite, apparently peraluminous with garnet formation.  I am interested in how the structures within the stone may have formed and its geological history.  
Any assistance would be most appreciated, thanks.  Barry Hunt
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Hi Barry,
I confirm Martin's view that Kashmir White (as far as I know most samples come in fact from Andar Pradesh state) is a typical garnet granulite, possibly former acid volcanics metamorphosed under granulite facies conditions. Orthopyroxene, diagnostic for granulite facies metamorphism is not present bed cause of the too high Al content of the rock. Interedsting is the fact that, in many samples, garnets are not evenly distributed in the groundmass, but concentrated along microshear zones (see top of attached photo), possibly the pathways by which granulite fluids (high-density CO2 and concentrated saline brines) have escaped during retrogradation. Jacques Touret
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I work on a Leica DMRXP in brightfield mode (for petrography), both using reflected and transmitted light. I have also 2 objectives which are suitable both for BF/DF. But when I switch the diaphragm module in DF mode I do not see anything. No light is sent onto the sample. Is there the need for a specific DF light reflector in the light turret, or is the BF reflector suitable ? Many thanks in advance for your answers. I would be happy to see pictures of the diaphragm module because I wonder if mine is correct.
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Dear Guenter, I know that the DF unit need to be pulled to the right, but when I do so, nothing happens... I wonder if a piece is missing on this unit, such as a round opaque lens, which would allow light to be scattered only around. But maybe the reflector is not suitable. In any case, many thanks!
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Spreadsheet/software calculating seismic velocities in peridotite as a function of mantle peridotite modal composition and chemistry of olivine/opx?  I look for spreadsheet/software enabling the calculation of seismic velocities on the basis of mantle peridotite modal composition AND composition of major minerals. Crucial is the possibility of translating the small variations of forsterite content (2-4 mole %) and corresponding orthopyroxene mg# to seismic properties. I wonder if it is possible...?
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I agree with the above. Moreover, the big trade-off will be with temperature (and pressure), too. Another significant uncertainty is anelasticity, which is a hard problem. A few % change in the mineral content will have a theoretical effect on the velocity, but whether you would be able to calculate a reliable value is a different issue. This type of thing has been done before, ignoring anelasticity (see below), but doing so ignores a significant effect on the velocities:
A composite geologic and seismic profile beneath the southern Rio Grande rift, New Mexico, based on xenolith mineralogy, temperature, and pressure
J.M. Hamblocka,b,!, C.L. Andronicosa, K.C. Millerb, C.G. Barnesc, M-H. Ren b , M.G. Averill b , E.Y. Anthony b
Tectonophysics 442 (2007) 14–48
doi:10.1016/j.tecto.2007.04.006
They provide extra calculation materials in a supplement and refer to a spreadsheet by Hacker and Abers (2004).
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Is petrography for micro-structural analysis of mortar and concrete?
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Dear Mr. Kunal,
Petrography is one of the most important research methods for the assessment of the technical properties of mortar and concrete.
The instruments for petrographic examination include substantially stereo microscopy, polarized light microscopy (transmitted light and reflected light), dark field microscopy, fluorescence microscopy, electron microprobe, scanning electron microscopy.
Here are a few examples of the examined properties:
1) qualitative and quantitative mineral composition of the rock aggregates
2) grain size of the mineral fragments, size of the rock fragments
3) grain shape of the mineral fragments, the shape of the rock fragments
4) pore volume of the mineral and rock fragments
5) fluid inclusions (liquid, solid, gaseous)
6) the degree of weathering and alteration
7) interaction of mineral and rock components with the binders
8) cracks and fractures in the concrete and / or mortar
9) relationship between crystallization and deformation
In the appendix you will find a publication in which I have examined, together with building engineers petrographic details of concrete, which is affected by damage caused by alkali-silica reactions.
Best regards,
Guenter Grundmann
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This granular (Fig. 1) is found in a shard of subaqueous basaltic tuff (Fig. 2). The tuff mainly consists of clinopyroxene and chlorite mineral clasts and shard. As shown in Fig. 1 and Fig. 3, the granular has three part: the darkest rim and core is chlorite, with low SiO2, low CaO, high MgO and Fe2O3. The gray part is epidote, with high Al2O3, high CaO, and low MgO. The light ring is likely sphene, with ~30% TiO2, ~30% CaO, and ~30% SiO2.
There is a small high CaO grain in the right like a door of the high Ti-Ca ring (See the CaO distribution map), possibly calcite. Some small sphene globules ejected through the door (Fig. 1).  
I am trying to explain this geological process:
The three-part chemical association was formed by chloritization of basaltic magma. The chloritization was faster than magma coolling because the seawater was heated to a very high temperature. When the chloritization (explosion and seawater-magma interact) occured, the melt was separated into chlorite, epidote, sphene and calcite, however, the granular was still hot that the core was still in liquid state. Then the sphene globules ejected into the core because of pressure difference...
Does anyone believe this? I am interested to hear your interpretations!
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Dear Mr. Sun,
the growth textures of concentric morphology are numerous and run the gamut from pegmatitic zonation through vesicles in basalts like that. They cover the supercritical and subcritical fluids. It is fundamental to know exactly what the different zones are made up mineralogically, and then take a look at the direction of growth (is it unidirectional...). Also keep in mind the size of the rings and zones, it will show you the quantity of the various components involved and last but not least are there breaks or hiatuses in the formation of the concentric shells which may direct your thoughts to different pulses. I know similar textures but feel unable of giving you a good explanation at this stage of investigation. It will only end up in a back- and-fro of speculations. The step "description" has not yet been solved to the extent to allow for a passage into interpretation. A cartoon showing all your information with regard to my recommendations will minimize the field of speculation.
Best regards
Harald G. Dill
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Thanks in advance for your replies.
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Dear Harald,
     Thank you for the papers once i complete the experimentation i would be sharing the thin section images.
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Hi everyone!
I am preparing some samples for XRD (X-ray diffraction) of marine sediments in the area of Mazotos bay, Gulf of Larnaka, Cyprus. Can anyone suggest some recent papers about the petrography and mineralogy of the source rocks in this area (sedimentary cover of the Troodos' ophiolite complex, Lefkara formation, quartenary deposits)? I am asking this, in order to be aware and to compare the existing data with my results. 
Thanks!
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Mr Towe
Firstly, i would like to thank you for your recommendation. Nevertheless, the reason i ask this question is that i prefer to have a clear view of previous field research and data in the area which i am going to provide my own work as a first step in order to compare the results after, without being biased of course. I think this will help me not to overrate possible wrong results and , on the other hand, to verify the correct ones.
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I want to apply this calibration to some granulites I'm working with.
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SOLVCALC might do the job:
Wen, S.and Nekvasil, H. (1994) SOLVCALC: An interactive graphics program package for calculating the ternary feldspar solvus and for two-feldspar geothermometry. Computers & Geosciences 20, No. 6, 1025-1040.
it is, for example, in ther list of software linked below.
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I'm working with granulites and I applied the thermometer of Ti-in-Biotite in my samples, the problem is that this is calibrated for 4-6 kbar rocks and T<800°C and I'm working with granulites of 7 Kbar and >800°C. The results I got from this thermometer are similiar with others thermometers as Ti-in-Quartz and Zr-in-Rt. 
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The criteria for using the thermometer are detailed on Henry's website at the link below. Here it states:
"Pressure range of the rocks should be 4-6 kbar - this is the P range of the calibration data set. (Based on evidence from a number of biotite experiments, samples equilibrated at lower P will have higher Ti and yield higher TIB temperatures whereas samples equilibrated at P>6 kbar will have lower Ti and will yield low TIB temperatures.)"
There is no information (there) on what the results will mean if T>800C. Providing the system is saturated in Ti (sounds like you have rutile present) it may be fine.
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In developing countries, there is still a general lack of interest in stone artifacts, and scarce cooperation of archaeologists with geologists. I find in French and anglo-saxon terminologies inadequate translations of siliceous rocks and there is no consistency in using specific terms. Therefore, the use of adequate and uniform terminology is still far from being satisfactory. It is very important to have a clear image and consensus about the meaning of a specific term. So, do you think that strict criteria can be established for distinguishing siliceous rocks?
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Even if the questions that are being asked may pertain to different characteristics of the natural material, it is important that natural materials are referenced in publications in a way that communicates the fundamental properties of that material, otherwise readers may misunderstand the significance of the materials studied or the questions being asked.  Mineralogy and lithology are two simple ways to identify materials; It also provides a way to link the archaeological study to regional studies of geology.
As an example with which I am personally familiar, referring to artifacts that are green hard stones all by the name of "jade" is misleading, even if many different lithologies are found to be in use in the same way that "true" jadeite-jade is used. Even if the archaeological or cultural use of green stones are considered similar to the use of jadeite jade, many green stones have vastly different material properties that will alter the complexity of the manufacturing process, the functionality of the final product, and the quality of that product. It will also alter how accessible the parent material is, which may cause the researcher to wonder about geologic sources and extraction techniques. Thus, the mineralogy and/or lithology may influence archaeological interpretations, and knowing this information at the onset of a study is valuable to both researcher and reader. 
For this reason, it should be important to researchers from diverse disciplines that study the same types of materials, albeit with different questions in mind, to utilize a common nomenclature; for example, identification of mineralogy and/or lithology is a basic and straightforward way to clarify many material properties of your artifact. Perhaps in the case of cryptocrystalline polymorphs of quartz, like chert versus chalcedony, the geologic vocabulary may not give much more information for asking archaeological questions. However, it will help clarify characteristics of the material for your readers, for example, which material is easier to manipulate or which is more durable. Furthermore, if you are interested in any provenance study of the artifacts, one cannot approach these questions without identifying the geologic origin of the material. 
although geologists may not ask the same questions, I would encourage collaborative efforts between archaeologists and geologists in order to identify materials according to one terminology. The researcher only has something to gain from making the research material more accessible to a wider audience.  
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I've seen ilmenite exsolution in orthopyroxene in granulites. I've been told that is an indicator of UHT metamorphism, but I still don't find a paper about it.
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First of all one must be sure that the exsolution hypothesis is correct, because intergrowths may be formed by other processes besides exsolution: co-precipitation, corrosion, breakdown of a pre-existing phase, eutectic/cotectic crystallization, a.s.o.. Ti solubility in orthopyroxenes is limited and decreases at higher pressure, so the exsolution hypothesis is not so straighforward. Relevant literature is not impossible to find, once the search is restricted to the occurrence of interest and more specific textural features. The Hayob et al. (1993) paper refers rather to ilmenite-orthopyroxene equilibrium thermometry. Please find attached two papers with chances to hit your topic.
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In my microscopic investigations on an andesite, I find a rather frequent mineral (please see the attached image), scattered as hypidiomorphic grains (size: 1 to >50 micrometer) with the following general composition (measured by SEM/EDS):
Fe: 20 to 37%,
Cr: 9 to 12%,
O: 29 to 48%,
Al: 4.5 to 12.5% 
+ variable amounts of Ti, Mg, Zn, Si, Ca
I can not figure out a name for the mineral (although have already checked webmineral.com).
I would be grateful for any help in this regard.
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Recalculation of your analysa to formula (Fe",Zn,Mg)(Fe"',Al,Cr,Ti)2O4 and ploting them to triangular diagrams Mg-Fe"-Zn and Al-Fe"'-Cr would help you to determine exact mineral name of your phases. I suppose that your crystals are zoned and there are represented at least two different minerals. This is typical situation for spinelides, which normally are very complex.
On photos given below you can to zsee zonation in crystals of zincochromite connected with their enrichment by Zn from core to rims.
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During my microscopic studies, I have observed numerous skeletal form magnetite grains in andesite porphyry rocks. I wonder under what conditions they have formed.
I already know that such skeletal forms of magnetite occur in some types of (ancient copper) slags, but in natural rocks they were rather new to me!
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Actually it has nothing to do with T and P, and only circumstantially with the cooling rate - essential being the high rate of crystallization (triggered by oversaturation) as compared to the ease of nucleation. Literature is vast, as a first step a very good basic explanation is here (and refs. therein): http://www.springerreference.com/docs/html/chapterdbid/3593.html
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I have done thin section, in photomicrograph seen grassy shape.
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Dear Pankaj,
Thanks for the reply. I strongly recommend testing the thin section using either XRF or EPMA to ascertain the mineral and glass content. The fibrous material may probably be some recrystallized clay mineral. The light grey fragments may be recrystallized feldspar which have to be confirmed by their optical properties.  I recommend the textbook: Ceramic Petrography: The Interpretation of Archaeological Pottery and Related Artefacts in Thin Section by P.S.Quinn as a starting point. Also see: http://scnapr.info/pottery%20website/Linked%20references /Shepard%20Ceramics%20for%20the%20Archaeologist.pdf for further information. Hope this answer helps you further.