# Mineralogy

Can anyone help with the determination of ternary regression equation?
I have a trivariate system for which component Z is highly dependent upon both the ratio between and the total values of components X and Y. When plotted on a ternary diagram (see attached) they form a very strong curvilinear relationship. Surely, there must be some way that a regression equation can be determined to calculate Z from X and Y. Can anyone help with this? None of the software I have is capable of a regression fit for a trivariate system, only bivariate fits.
Pietro Armienti · Università di Pisa
The fact itself that a triangular plot lays in a plane states that the plot has only two degrees of freedom. This is evidenced by the fact that the three values have a constant sum: Freedom= variables-relations. Provided that triangle vertices have the binary coordinates A (0,0) , B(50,100cos(30)) , C(0,100), the X,Y coordinates of point P of ternary coordinates (a,b,c) are X=b+c cos(60°) and y=c cos(30°). Regression criteria follow in a strightforward way...
Could you tell mineral name for given composition "SiO2=16.523, FeO = 64.942,Na2O=2.375,K2O=1.602,CaO=0.943,MgO=0.140,Total 87. 999.
rock name is Grt- Bt Schist, analysed by EPMA and i wants to know the mineral name for given above the composition.
Madhavan Kaliappan · Indian Institute of Technology Bombay
Alexy Berezin, but this mineral properties under PPL brown in color, moderate relief, in crossed nicols Isotropic. EPMA thin section BSE image of this mineral showing zoning pattern. I am feeling, the optical properties are not match with Cronstedtite.
Is it possible to differentiate Ortho- and Para-amphibolites based on geochemistry?
We have amphibolites which clearly show sedimentary structures like bedding planes and are associated conformably with other sediments like greywackes, banded iron formations, dolomitic limestones and impure quartzites. Also, they consist of detrital quartz grains. The amphibolites mainly consist of tabular and prismatic hornblende and sub-rounded to well-rounded quartz set in a meager fine grained matrix of quartz, chlorite and sericite. But they have negligible felspars and when plotted in chemical classification diagram they fall into ortho-(igneous) amphibolite category. So is there any way for classifying the aphibolites into Ortho (igneous) and Para (sedimentary) amphibolites.
Chandan Kumar B · Karnatak University, Dharwad
Dear Licht, I totally agree with your opinion. But shouldn't there be any hidden facts/clues, which can be used to overcome these confusions?
How can I distinguish between naturally occurring zeolite and a synthetic one?
If I have a zeolite sample of an unknown source, what are the best first steps to characterize it and to determine whether it was a synthetic or naturally occurring mineral?
M.Cemal Göncüoglu · Middle East Technical University
We worked on characterization of different commercial materials and natural zeolitic tuffs from Turkey. My answer was just a practical approach for discrimination.
Can exfoliation of vermiculite or hydrobiotite be done by microwave in a large scale?
Exfoliation of vermiculite
Peyman Hm · Shahid Bahonar University of Kerman
Thanks to all.
What causes the voids in zircon grains?
During the internal textural analysis (BSE images) of zircon, I observed a perfectly rounded voids which may not contains any mineral. And mostly they are large as 1-5 micrometer in diameter. Sometimes internal textures occur around this void. And sometimes more than 5 voids can be seen in partially recrystallized detrital cores. Is there any interpretation for this voids?
Richard Taylor · Curtin University Australia
Hi There, Be aware that you probably have the BSE turned up nice and high to get your images, so make sure they are actually voids (e.g. use SE imaging) and not mineral or melt inclusions. If they are voids of that scale then one guess would be volume expansion from alpha decay. This can cause a variety of cracked textures, which if reannealed can appear as voids within the grain. The next obvious one, as mentioned above, would be fluid alteration. dissolution-reprecipitation for example will tend to expel trace elements and leave behind a more 'pure' grain, which will therefore have a lower modal volume. I would reccommend looking at some papers from Thorsten Geislers zircon work, or the Frank Tomascek paper in JPet on Syros zircons for good textures of this kind. As always, an image would be good, and extra info such as SE, CL, rock type etc Rich
Is this Chloritoid in the attached photomicrograph?
It is pleochroic and greenish in color in plane-polarized light (PPL) and it is dark yellow to greenish pink color in cross-polarized light (XPL) as it appears in the photograph. Is it Chloritoid? I also thought it could be tourmaline.
M.Cemal Göncüoglu · Middle East Technical University
Agree, just rotate the table about 45 deg in both directions and see what happens.
Does anyone have information about protocols for nitric acid etching on opaque microcrystals?
I wish to enhance the visibility of the successive growth phases of opaque crystals (mostly pyrite ; 5-200µm) in optical microscopy thin sections. I understand I have to use nitric acid etching. Any suggestions as to how?
Axelle Hubert · CNRS Orleans Campus
Is there a scientific explanation for the greenish colour of rock "charnockite"?
Charnockite is an opx (usually hypersthene), quartz and feldspar bearing meta-igneous rock, mostly acidic in composition, and metamorphosed under granulite facies conditions. It is commonly found in Gondwana fragments such as in Sri Lanka and India. One of the key characteristic features of chranockite is that minerals of feldspar and quartz in the rock have a greenish appearance. Is there any scientific explanation for the cause of this colour?
Geoff Grantham · Council for Geoscience
Feldspars can accommodate a small substitution of Al by Fe3+ which can contribute to the red colour in feldspar. One wonders whether reduction of such Fe would not similarly contribute to a different colour. McIver J took "dark green" charnockite (unaltered) and placed it in an acid solution for a period of time after which the charnockite last its colour - re analysed the rock and concluded that Fe contents had been reduced. McIver, J.R. (1963) A contribution to the Precambrian geology of southern natal. PhD thesis. (Unpubl) Univ. of Witwatersrand. 203pps.
Are there any publications about REE contents in plagioclase, biotite and pyroxenes in alkaline felsic rocks, obtained by LA-ICP-MS?
I've obtained data by LA-ICP-MS, and now I'm looking for data to compare my results, and whole process of analyse.
Dejan Prelevic · Johannes Gutenberg-Universität Mainz
Here you have some data on Mediterranean alkaline rocks, for phlogopites: Petrological characterization of the mantle source of Mediterranean lamproites: Indications from major and trace elements of phlogopite T Fritschle, D Prelević, SF Foley, DE Jacob Chemical Geology 353, 267-279
Is it possible to obtain bulk Raman Spectra for the traverse of a 2 cm rock chip?
How complicated can the procedure be? We aim to map serpentinite mineralogy on a regional scale and are trying to find method for quick and reliable identification of serpentine polymorphs in a rock chip. It has been demonstrated that Raman spectroscopy allows one to distinguish between antigorite, chrysotile and lizardite. Does Raman spectroscopy provide an opportunity to get bulk scan spectra e.g. for 2 cm traverse in a rock chip? We need to be able to then pick signatures of different serpentine polymorphs from bulk spectra and by that see which phases are present.
Souvik Das · Wadia Institute of Himalayan Geology
It is possible as it is said above. But if you want a modal percent of the lizardite, chrysotile and antigotite through Raman mapping in a 2 cm rock chip, that could be really a tricky job.
What is the effect of seawater on U partitioning in ultramafic minerals? What literature papers document this?
I have constructed trace element budgets between mantle minerals olivine, orthopyroxene and clinopyroxene for about 20 abyssal peridotite samples. There is clear partitioning for Pb, Nd and Yb among the mineral phases, but it is not systematic for U. There must be some secondary process like seawater alteration or serpentinization that causes what we observe. Are there any references in the literature for this effect on U?
Eric Hellebrand · University of Hawaiʻi at Mānoa
Hi Megan, cooool study. Nd and Yb are not surprising, but I'd love to see your Pb data! U is not as bad as B, and appears to be mainly affected by "seafloor weathering", rather than "serpentinization". In Margot Godard's EPSL paper on the 1520 perids, you can see how the abyssal peridotites have ppm-level U, and the drillcores have ppb level U. I think it's the Mn-Fe-oxides, but am not aware of any studies that have focused on this... http://dx.doi.org/10.1016/j.epsl.2007.11.058
Is there only Montmorillonite Minerals in claystone or mudstone whice cause "liquefaction" or subsidence problem? If not, what else?
I want to know about the minerals which cause "liquefaction" problem, especially in Indonesia.
Aria Tsam · Aristotle University of Thessaloniki
hi.Try to visit the sites: 1-http://etheses.dur.ac.uk/9085/1/9085_6016.PDF
What is the best method to prepare (digest) and analyse sapphire samples?
Can we use ICP-OES methodology to analyse impurities in sapphire samples (used in ceramic industry)? We have microwave digestion oven and ICP-OES available in our lab. Thanks in advance!
Roseli Gennari · University of São Paulo
I am used to digest, silicate samples, including sapphire with microwave digestion systems, but, the equipment must operate in high pressures and so you have to pay attention on the security aspects. About fusion, you may have problems with some interference on analytes determination.
Is there any method to discriminate the source of sediments from igneous and metamorphic rocks from a geochemical point of view (other than mineralogical)?
From the XRD study, the samples show the presence of sillimanite, andalusite, garnet kind of minerals. None of the other petrographic information is available. Hence, I need to know the possibility of the major, trace and or REEs to show the source discrimination from igneous to metamorphic.
Narasinga Rao Kesavaraju · Osmania University
I fully agree with the information given by Dr.L.R.K. Perera. Presence of metamorphic minerals like sillimanite and andalusite indicate the source to be metamorphic. Tryiing to know the protoliths of these minerals before metamorphic formation of these minerals, probably -in my opinion is rediculous. Miss Resmy has not indicated about the age of the sedimentary formations she is dealing with. If they are of Archean it is much more difficult. In a way -the protoliths (i.e., primordial rocks) for all rocks will be igneous. When dealing with sedimentary rocks -in my opinion- the identification of the source areas based on petrographic study (including XRD- if all minerals can not /could not be identified) should be sufficient for meaningful interpretations. Trying to know the source material for the metamorphic minerals -i.e., whether igneous or metasedimentary or meta-igneous does not lead to anywhere - unless one wants to know the origin of the earth from the mineralogy/chemistry of material found in seiments. That will be beyond the scope of study of sedimentay rocks of a given area. Afterall, some of the clayey material mentioned by Dr.Perera (and mterial for other minerals)could have come extra terristrial source -as lot of cosmic dust has been falling on earth and in the oceans. Fertile imagination should stop at reasonable point/stage. Besides, it is not clear as to what is the exact research problem/topic of the researcher. Dr. K.N.RAO
What is the length of the longest known quartz dyke?
I am working on quartz dykes in Malaysia and I need to do some comparison with other quartz dykes in the World.
Vincent Thiéry · Ecole des Mines de Douai
Hello, In France I know a dyke, cropping out more or less continuously, of 6-8 km long for a few 10 - 50 (?) m wide, but the only references I know are in French. Do not hesitate to contact me for further information.
What is the concentration of gold in basalts from Emperor seamount chain (Detroit Seamount)?
What is the concentration of gold in basalts from Emperor seamount chain (Detroit Seamount)? I cannot find articles about it.
Pavel Mikhailik · Far East Geological Institute
Thank you Walid! I found many information about land gold deposits of Pacific ring Hawaiian basalts are contain 2.4-2.7 ppb of Au. I can not find concentration of gold in intraplate basalts of the Pacific (seamounts of the Emperor volcanic chain (N-W Pacific)).
Can we use the gamma ray spectroscopy for determining the age of rocks or different layer in mountain?
The existence of Ra-226, Ac-228 and their families were positively detected
Alan Cresswell · University of Glasgow
I wouldn't have thought so. Normally dating using the proportion of isotopes in the natural decay series is done on separated mineral grains, you need to ensure that the parent and daughter isotopes can't move in and out of the sample. You then have samples which are too small for gamma spectroscopy measurement, even if there were convenient gamma rays to allow quantification of the different isotopes in the decay chains. Mass Spectrometry would be the tool of choice on such samples.
Is it possible that a weakly silicate-saturated magma will evolve to a silicate-undersaturated magma?
I have some rock samples from an alkaline felsic complex. Their geochemistric characteristics show an evolution trend from weakly silicate-saturated rock (modal Qtz <5 vol%) to silicate-undersaturated rocks (modal Ne>20vol%). This is different with what l know before. Is this possible? Which mechanism can explain it?
Martin Menzies · Chinese Academy of Sciences & Royal Holloway, University of London
Yu Sheng, I have just posted "High level triggers for explosive mafic volcanism: Albano Maar, Italy" on RG. This reports the possible effects of high level addition of CO2 (limestone assimilation) in changing the fractionation trends of silica undersaturated magmas (as Morten points out) from phonolitic toward foiditic derivatives.
Why platinum elements and minerals are relatively less in ophiolitic chromites?
Platinum Group Elements (PGE) and Minerals (PGM) can be found as part of the chromite composition and inclusions respectively. However, chromites of the ophiolitic peridotites consist of relatively much lower PGE and PGM (esp. Platinum) than those of the layered intrusion peridotites. Is there an explanation for this phenomenon?
Elkin Hernández Ríos · University of Chile
How to distinguish between a Fracture Trace and a Foliation Structure in a digital image?
In rock surface stereophotogrammetry and in digital borehole imaging the small opening of a single fracture trace often stays in subpixel scale, and can therefore not be solved in a straight forward way.
Are chondrites the ultimate reference?
Chondrites are believed to be the least modified most pristine material left over after the formation of the solar system. Geochemists make use chondrites as their ultimate reference and carryout a chondrite normalization of their analyses and isotope geochemists compare isotopic evolution of chondrites with that of their samples. I want to know the pros and cons of this practice and whether it is really meaningful.
L. R. K. Perera · University of Peradeniya
Thanks Tim, got it.
What are the better barometers that I can use for garnet and biotite absent orthopyroxene bearing gneiss?
Om Prakash Kaptan · Indian Institute of Science Education and Research Kolkata
I think you can use Fe-Ti exchange in two Fe-Ti oxides (ie. Ilmenite-Magnetite). Solvus thermometers can also be used like Muscovite-Paragonite for K-Na elements.
Does the presence of very growen crysrals of quartz in granite rocks point to the presence of native minirals like gold?
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Mahaveer Sisodia · Jai Narain Vyas University
There are pathfinders (chemicals or elements) for the exploration of minerals....look for them......Grown crystals of quartz in granites point more towards placement of granites!!
Is there a way of removing organics from naturally-sourced minerals?
I need to remove any background organic signatures but do not want to alter the mineralogy by furnacing. Does anyone know of a method involving radiation?
John Janks · Weatherford Laboratories
Hopefully, we will be allowed to publish a method developed at our labortories using surfactants. It is performed at 50 C, and to date we have found no negative influence on the clay mineralogy, including the smectites. You are asking a long-standing problem that has needed an answer for decades. If we get the OK, I'll make sure I publish a link on ResearchGate.
What is the role of clay minerals in the distribution of trace metals in marine sediments?
Among the clay minerals, which is the most adhesive in nature? In coastal, estuarine and marine sediments, what is the role of clay minerals in the distribution of trace metals?
John Janks · Weatherford Laboratories
In my experience the smectite (aka montmorillonite) family predominates the clays as well as other sedimentary minerals. They happily allow most elements in the +1, +2, or +3 state into the interlayer spaces, where you will find them on a chemical analysis. Furthermore, smectites allow elements such as Mg, Mn, Al, Si, Ni, Zn, to enter the tetrahedral or octahedral lattice. Chlorites have a similar capacity to exchange Fe for Mg, but these are usually diagenetic events, not occuring at surface conditions.
Garnet in igneous rocks - can anyone help?
I am looking for papers and ideas on garnet in igneous rocks (e.g. tonalite, granodiorite, diorite, aplite, pegmatite) and I will be thankful to have any comments on this.
Hi, check this paper for pegmatite, there are several paper citing this one. Petrogenetic implications of magmatic garnet in granitic pegmatites from Southern Norway (http://canmin.geoscienceworld.org/content/50/4/1095.short) Good Luck,
Has anyone come across O-isotope fractionation data for braunite?
I analyzed some braunite samples for O-isotope compositions during my MSc but could not find experimental data to compare my results to.
Brenton Fairey · University College Cork
Braunite is also a bit of a strange mineral given the amount of Si it contains.... in terms of concentrations it puts braunite somewhere between an oxide and a silicate! So it is even difficult to try and relate it to fractionation curves of hematite for example.