• Sarwan Kumar Dubey added an answer:
    What is possible alternative to gypsum for ameliorating alkali soils?

    Gypsum being mineral in nature and mined from limited area in India, its availability n future will no longer be the same as it was in the past. Therefore there is an urgent need to find out an alternative to mineral gypsum and standardize the agro-techniques for its use on sodic soils.Your comments and suggestions on this are invited.

    Sarwan Kumar Dubey

    Thanks @ Karl-Jan Erstad for this wonderful link and email ID of Mr Dastol.

  • Graham Wilson added an answer:
    Can anyone ID this mineral in reflected light? I have SEM data to help and I'm still confused?

    Little info:

    -These grains have been tested in the SEM with the EDAX attachment and the data reads as the following (on average):

    20 - 25 wt. % Na, 20 wt. % Zn, 20 wt. % S, 5 wt. % Au

    The rest of the total 100% is oxygen and carbon with trace elements filling up the rest.

    This is an incredibly high amount of gold and I'm pretty sure that it is some kind of ZnS sphalerite, but the amount of Na is seriously throwing me off.

    -p.s. the grains I'm talking about are the lighter grays with inclusions of some metal I'm unsure of.

    + 3 more attachments

    Graham Wilson

    In reflected light this certainly looks like sphalerite with exsolved CuFeS2 ("chalcopyrite disease"). You don't mention either Cu nor Fe in the averaged analysis, but even if the exsolved blebs are (say) pyrite not chalcopyrite, there must be some Fe. If this is the unusual sphalerite with negligible Fe, then it should be essentially colourless in transmitted light. I use polished thins for most of my work, because of the "complete" picture one gets from optical properties in transmitted and reflected light. I don't think you mentioned the diameter / area of the analysed region, but I'm pretty sure the Na (and Au) are analytical issues as inferred by Ian.

  • Phil Bailey added an answer:
    Does anyone know what kind of symplectite this is?

    In some thin sections I'm working on I've noticed a type of intergrowth in clinopyroxene. The symplectite is usually partially or completely enveloped in another grain of clinopyroxene. In the picture I've attached to this post you can see a yellow/greenish grain of cpx surrounded by a first order gray cpx. It appears as though the yellow cpx is replacing the gray cpx, which leads to the formation of the symplectite. Does anyone know what this is?


    Phil Bailey

    This should help nicely  https://wwwf.imperial.ac.uk/earthscienceandengineering/rocklibrary/viewglossrecord.php?gID=00000000178

  • A. Mouraz Miranda added an answer:
    Calculation of norms?

    Does anybody have a program or worksheet to calculate the norms of a spinel lherzolite using the calculation schemes of Kelemen et al. (1992, Nature). The same method has been followed by Walter (2003, Treatise on Geochemistry). Thanks. 

    A. Mouraz Miranda

    I have used rittmann rules forty years ago!

  • Saeed Abbas asked a question:
    Gypsum is formed mostly in shallow marine environment. But any evidence/possibility of gypsum formation in deep marine basin?

    Gypsum is formed mostly in shallow marine environment. But any evidence/possibility of gypsum formation in deep marine basin?

  • Yongfeng Wang added an answer:
    Calculation of norms?

    Does anybody have a program or worksheet to calculate the norms of a spinel lherzolite using the calculation schemes of Kelemen et al. (1992, Nature). The same method has been followed by Walter (2003, Treatise on Geochemistry). Thanks. 

    Yongfeng Wang

    Thank you very much for recommending me thses papers. 

  • Gönenç Göçmengil added an answer:
    What is the relationship between the Philippine Sea Plate and the East Pacific Ocean crust?

    What is the relationship between the Philippine Sea Plate and the West Pacific Ocean crust?What is the relationship between the subduction zone in East China and the subduction zone in East Mariana?

    Gönenç Göçmengil

    As far as i know, one of the most comprehensive work on the area have been done by Robert Hall; you can check his paper from the link:


    but i'm not sure if there is any recent review article with new datasets

  • Ian J Slipper added an answer:
    What is the most suitable coating material (conducting material) for SEM analysis of coal samples?

    We coated coal samples with a thin layer of Au (Sputter coating). Due to nature of samples (>60 wt.% C), it is very hard to find minor minerals. Although we analysed samples thoroughly, but we did not find any mineral (such as quartz, pyrite, calcite, and oxides) other than a clay mineral?? with a very characteristic peak of Nb (using EDS) (please find the attached file) and smaller peaks of Mo. 

    I wonder whether the nature of coating material could change (influence) the resolution of SEM. could some coating materials mask the resolution of SEM-EDS and make it harder to find other minerals?

    Thank you 

    + 1 more attachment

    Ian J Slipper

    Very good comments above. Just to add about the sample preparation method. If you have coals you will need to vacuum impregnate the sample with a low viscosity resin that is stable under an electron beam. Polishing will then need to be done very carefully. Best if you can find someone who has experience in polishing this type material to start with - or have fun trying! Yes, use carbon to coat. One problem you may encounter is the size of the particles being too small. Your image 4-1 shows a 2um particle - be aware of the size of the interaction volume; you will likely be including x-rays from elements outside your area of interest.

    One reason your software may be giving you incorrect peak identifications is the number of counts in each channel, you maximum is only 500 counts. This is nowhere near enough in order to gain correct peak shapes for auto identification (humans can do better with few counts ;-) I don't know what detector you have but with a Si(Li) detector we used to work at 2,500 counts per second on the cobalt standard and count for 60 seconds for good quant work. These days with faster detectors it can be done in few seconds gathering 10s of thousands per second. So look at your data acquisition strategy.

  • E. Yalçın Ersoy added an answer:
    Meaning of silica saturation in igneous rocks
    Despite being commonly used for more than one century, the concept of silica saturation has not yet reached a common definition.

    According to igneous petrologists dealing with magmas, a silica-undersaturated melt is characterized by nepheline-normative compositions, a silica-oversaturated melt is characterized by quartz-normative compositions and a silica-critically saturated melt is free of nepheline or quartz in the CIPW norm, having olivine-orthopyroxene-normative compositions (being also defined as albite-normative).

    According to igneous petrologists dealing with mantle residua (peridotites) a rock with olivine and orthopyroxene (e.g., the classical shallow mantle assemblage plus other minor phases) is to be interpreted as silica-undersaturated composition (because of the presence of olivine). I disagree with this last definition.

    According to me a rock with modal or normative olivine-orthopyroxene is to be classified as critically saturated rock. In the classical basalt tetrahedron of Yoder and Tilley, silica-oversaturated compositions plot in the SiO2-Pl-Cpx-Opx field, SiO2-undersaturated compositions plot in the Ne-Pl-Cpx-Ol field and SiO2-critically saturated compositions plot in the Pl-Cpx-Ol-Opx field. Am I right or what?

    I have been said that the concept of silica saturation is different if dealing with mantle residua or partial melts. For me this is a concept that can be adopted in the same way in both cases.

    In other words: The shallow Earth's mantle is made up of SiO2-critically saturated rocks (strictly speaking metamorphic, not igneous rocks).
    E. Yalçın Ersoy

    Hi Michele,

    I think you're completely right. I think those rocks with ol + opx should be named as Si-saturated (critically). 


  • G. G. J. Ernst added an answer:
    Could anyone clarify what may be Zircon saturation levels in Laacher See magmas ?


    The Zr melt concentrations in the Laacher See Magma Reservoir have been estimated by Hans Schmincke and coworkers to be in the range of hundreds of ppm (ULST), O(1000ppm) (MLST) and around 3000 ppm (LST) for the lower H20-undersaturated, middle, and upper H20-saturated compositionally zoned magma chamber respectively.

    I wonder how this may relate to Zircon saturation curves. Such curves have occasionnally been constrained experimentally for certain magma compositions (work by Mark Harrison, Bruce Watson and coworkers) but I am finding it difficult to translate how this may relate to the case of the Laacher See magmas.

    Zircon solubility appears to be related to Zr concentration, Temperature and magma composition including SiO2 and TiO2 concentrations and the alkali/alumina index (eg. Harrison et al 2007) and one may also expect that it  also depends on the amount of dissolved volatiles (eg. water) in the melt.

    I cannot find relevant papers which would enable to assess for what conditions Zircon saturation may be reached for the 3 end-member compositions of the zoned Laacher See magma chamber (or in a presumed basanite parent magma at LSE).

    What intrigues me is that Zr contents seem to me to be very high at Laacher, yet Zircon occurrence seems to be "rare" and restricted to mostly very small zircon crystals in LST pumices and to some rare occurrences of sometimes  larger crystals (typically mm-sized xtals) in some cumulate nodules from LLST and MLST (eg. Schmitt 2006).

    Is it that a large melt  H20 content suppresses Zircon crystallisation ?

    Or that Zircon crystallization rates are too low in general in the LSE magma conditions  ?

    I would be grateful for any insights into Zircon saturation and Zircon crystallization rates and what may control them at Laacher See (P: 115-200 MPa; H20: 2.5-5.7 vol% or so), or in basanite-tephrite magmas under crustal conditions.

    I am also interested in any insights for Thorite crystallization in LSE magma conditions or in basanite-tephrite magmas under crustal conditions.

    Thank you in advance for any suggestions or insights.

    Happy New Year and Best Wishes,


    G. G. J. Ernst

    Dear Gerhard,  Thanks a lot for all these info. Regarding the large Laacher See zircons, I fully agree with your pegmatite hypothesis and I have scanned a photo of a zircon that supports this - indeed you have already suggested similar observations you have made yourself. On the other hand for the large zircons in the older tephrite lavas I am less convinced that the same process could work (no obvious resorbption features). I'll attach the two scans to illustrate the contrast asap, in the coming days most probably.

    Thanks again for the discussion and for the ref.

    Beste Grüsse,


  • Oladotun Afolabi Oluwajana asked a question:
    What are the implications of Telocollinite and Desmocollinite macerals in shale samples?

    Ten 10 of the samples analyzed have values that range from 0.45 - 0.61 while 3 samples range from 0.51 - 0.59. I assume the samples analyzed are more of hydrogen - poor vitrinite A. I need more enlightenment on the subject.

  • O. Robach added an answer:
    What does the so-called IPF-colouring in orientation maps actually denote?

    Crystal orientation maps, e.g. derived by EBSD, are often displayed in so-called inverse pole figure (IPF) coloring. Do these maps (often three maps are displayed for reference direction X, Y and Z) really reflect the locally discovered orientation, or do they insert additional symmetries which reflect a higher symmetry and therefore perhaps another not-symmetry-equivalent crystal orientation?  

    O. Robach


    For the FCC I came across the case when the "normal" crystal and one of its sigma3 twins give exactly the same colors in the three inverse pole figures.

    This happens when the [111] twinning axis is along X, Y or Z.

    This is because the orientation matrix used for calculating the color for the x axis is rotated so as to bring either x or -x in the first stereo triangle.  (using only rotations x will not always fall in the first triangle)

    NB : if somebody could tell me where to find the calculation for the orientation colors for the monoclinic it would help me a lot.


    Best regards


  • Sobhi Nasir added an answer:
    How is a mineral identified from EPMA data? Is there any standard formula, accommodating the wide range of compositions like olivine or pyroxene?

    I am a beginner, so I do not know about the existing procedures for converting chemical composition from EPMA to identify the mineral. I would like to know the general procedure followed. 

    I am working on EPMA data of micrometeorites and have several points of data for each sample, along with BSE images. I am interested in identifying which minerals are present in each sample, which are generally Olivine or Pyroxene. However, due to the wide range of compositions of both Olivine and Pyroxene, with a significantly overlapping composition ranges of Fe, Mg, and Si, I am unsure about how to definitely identify the mineral.

    Sobhi Nasir

    Most minerals have a fixed range of SiO2, MgO and CaO content. For olivine SiO2 ranges between 38-42 wt% and MgO between 40-50 wt% and very low CaO<1%. In comparision Orthopyroxene and clinopyroxene have higher SiO2 % 50-56%. Cpx has high CaO 17-22%, lower MgO. From the EPMA data you can decide your minerals if they are olivine or pyroxene by looking at their SiO2, MgO and CaO content, then you can calculate the formulae using many programs available in the web for free

  • Victor Ostrovskii added an answer:
    What types of organic polymers made or found on Earth have affinities to those found in insoluble organic residues from carbonaceous meteorites?

    Insoluble organic matter residues are the remaining insoluble organic material after extreme acid digestion of the extraterrestrial material. They contain complex morphologies that exist as either: isolated spherical compounded shapes; hollow spherical objects or irregular (non spherical) shapes which internally often contain the same conglomeration of spherical features. Please see attached DF STEM images of some of these morphologies from two organic rich carbonaceous chondrites. As the residues are a product of the removal of surrounding mineralogy (i.e. context in situ is lost), connected features on the submicron to micron scale in the images, by approximation, should only be considered. Thanks!   

    Victor Ostrovskii

    Dear Hitesh,

    As for the direct answer to your question, this is a case when I agree with Dr. Kenneth M. Towe.

    If you are interested in the theory of living-matter formation anywhere in Universe, I advise you the works on the LOH-Theory. The publications are available in my pages at the ResearchGate site. 

  • Marlina Elburg added an answer:
    How can I calculate the Nb/Ta ratio of the residual melt after muscovite crystallization using the model of Rayleigh fractional crystallization?

    In the paper "The key role of mica during igneous concentration of tantalum" contributed by Stepanov et al., (2014), they summarized that "crystallization of 99.9 % of melts precipitating 10 % of muscovite might increase Ta/Nb by a factor of 8 and concentrate Ta to 760 ppm in the residual melt. I am confused how they get this conclusion and how they calculate that. I used the equation for Rayleigh crystallization but failed to get the same value.

    Marlina Elburg

    The calculation seems roughly correct. They use DNb =3.5 and DTa = 0.4 in muscovite. If the fractionating assemblage contains 10% muscovite, then the bulk D is 0.35 for Nb and 0.04 for Ta (assuming the other minerals do not take up any Nb or Ta, which is of course an oversimplification). The fraction of liquid remaining is 0.001 (as the crystallised fraction is 0.999). for Nb: Cl/C0= (0.001)^(.35-1) = 89. For Ta: Cl/C0 = (0.001) ^(0.04-1) = 759.

  • Roger Spurr added an answer:
    Can we see Fe2O3 in Sillimanite?

    Is it possible to have Fe2O3 in Sillimanite?   I observed (under SEI) a sillimanite looking grain (in a metamorphic rock sample)  with characteristic cross fractures in my SEM-EDS studies. But several points along the very same grain show the following composition;

    Alumina - 58 - 61 wt%

    Silica - 35-38 wt%

    FeO+Fe2O3 - 3 -5 wt%

    Is this gain is sillimanite or something else. Is it possible Alumina to be replaced with Fe2O3?

    Thanks in Advance!

    Roger Spurr

    I believe rocks are the mineral bodies of sublimated creatures. https://www.youtube.com/watch?v=GVWSopgKzMU

  • Tayyaba Mateen asked a question:
    Can anyone tell me why a .ang file saved in TSL OIM Analysis (from an original .osc file) cannot reopen in the same program?

    I want to work on both .osc and .ang files in MTEX for calculating seismic properties of micaceous minerals. MTEX needs both formats. However, when I export the raw .osc file data (acquired using TSL Data Collection S/W) as .ang format in TSL OIM Analysis S/W, it saves as a .ang file, but never reopens in the Analysis S/W again. It gives the error: Cannot read phases from the .ang file, invalid symmetry.

  • Atula Senaratne added an answer:
    I'm working on an urban inland lake experiencing acidification as a result of oxidation of ASS. What is the mineralogy/nature of the 'oil-like' spill?

    I've noticed this visual attribute is a known indication of oxidised ASS. But I can't find any information on the geochemical nature of the material.

    From the academics I've spoken to, they hazard a guess at it being an extremely disordered Fe-oxyhydroxide. Another suggestion included organics as a component due to the shiny-ness of the film.

    Just wondering what other thought?

    XRD analysis was performed on a sample yielding a mineralogy of vivianite, gypsum (both of these appearing in several other samples), then pyrite, ankerite and Al, which were unique to this sample. However there was a very high noise level on the pattern trace for this sample, so the reliability of these results are in question.

    I've attached a pic. any help would be greatly appreciated as I'm so very curious.

    thanks heaps

    Atula Senaratne

    Hi Anne-Marie

    I experienced a similar bacterial film in water purification systems involving high level of dissolved iron. This bacterial froth is beneficial where it can scavenge many other unwanted things such as heavy metals.



  • Aurelio Sanz Arranz added an answer:
    Is this mineral really Kemmlitzite?

    See the mass spectrum and the SEM image below.

    Thanks for your help.

    + 1 more attachment

  • Aurelio Sanz Arranz added an answer:
    How do I identify planar deformation features in olivine?


    Can anyone assist me in identifying the following texture in olivine? The rock comes from a confirmed meteorite impact site and I suspect it might be planar deformation features. However I have no experience with PDFs so I might be completely wrong. If someone can provide literature with clear descriptions of PDFs in olivine it would also be very helpful.

    Your assistance is greatly appreciated!

  • Vyacheslav Lyashenko added an answer:
    Where can I find a database of images are made under the microscope?

    I'm interested in images of minerals, rocks, soil, cement, polymers ...
    It is desirable that there is a description of such images (under a microscope).

    Vyacheslav Lyashenko

    Thank you very much, dear Patrick.

  • Narasinga Rao Kesavaraju added an answer:
    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.
    Narasinga Rao Kesavaraju

    I fully agree with Prof. Stephen Kraus suggestions/observations.  I am sure you may find chilled margin(s).  Many people somehow over look this aspect.  Also, can you send /show a photomicrograph of the amphibolite?  I wonder whether it could be an ultramafic rock retrograded to amphibolite. KNRAO

  • Emmanuel Sakoma added an answer:
    Can anyone suggest a reliable chemographic diagram for representing meta-aluminous granite?

    The granite is meta-aluminous calc-alkaline with ilmenite, epidote, sphene, biotite, hornblende,plagioclase, microcline (megacrsyts) and quartz (Silica saturated) assemblages. The granite have mingled with basic magma to variable degree. Your suggestions will be valuable and helpful. 

    Emmanuel Sakoma

    From what you are explaining, you'd have to use approaches such as Shreinemakers:

    ZEN, E-an (1966): Construction of pressure-temperature diagrams for multicomponent systems after the method of Schreinemakers : a geometric approach. Geological Survey Bulletin, 1225.

    OR use some of the thermodynamics software for mineral equilibria in a peraluminous system (from calculation of mineral activities):

    BALDWIN, J. & MOGK, D. Advanced Modeling Programs: Introduction to the THERMOCALC Mineral Equilibria Modeling Software. Http://serc.carleton.edu/research_education/equilibria/thermocalc.html

     Or visit


     I do not have much experience in these; other paers by Calvin Miller (etc), locatable through "Googling" might be of help as well.

  • Masoud Ovissi added an answer:
    What would be the best approach for finding the Genesis (Origin) of Copper deposit?


    I am making proposal on Aynak Copper Deposit, Afghanistan. The genesis for Aynak Copper Deposit is proposed as sediment hosted syngenetic deposit but there are some points (have Intrusion which is felsic to mafic in composition, also the source of magma is unknown whether it was fertile or not) which I think is epigenetic hydrothermal deposit.

    I have no idea what would be the possible approach (methodology) to find whether it is Hydrothermal deposit or not. Also mineralogical and geochemical investigation of both mineralized and unmineralized rocks would be helpful for finding the hydrothermal source?

    Best Regards
    Wasiq Lutfi


    Masoud Ovissi

    Dear Wasiq,

    In attachment you can find two other parts of USGS reports entitled:

    Analysis of Imaging Spectrometer Data for the Aynak-Logar Valley Area of Interest


    Geohydrologic Summary of the Aynak Copper, Cobalt, and Chromium Area of Interest.

    Best Regards,

    Masoud Ovissi

    + 1 more attachment

  • Harry ten Brink added an answer:
    Magnetite in fly ash are derived from decomposition+high temp. oxidation of pyrite in combustion boiler. Is decomposition = complete pyrite melting?

    In description of fly ash mineralogy it is frequently stated "magnetite crystals in fly ashes are derived from decomposition and high temperature oxidation of pyrite of feed coal in combustion boiler." What does decomposition mean? Is it complete melting of pyrite grains in boiler? Or solid state transformation of pyrite to magnetite without involving melting of pyrite (m.p. of pyrite- about 1180 deg. Celcius)?

    Harry ten Brink

    Decomposition means that the pyrite FeS2 first becomes FeS, while the "second" sulphur leaves as a gas and is oxidized to SO2

    FeS (pyrrhotite) then oxidises

    FeS is a liquid and the particles become droplets and therefore the iron-oxide particles are also spherical.

  • Sobhi Nasir added an answer:
    What's the groundmass of this volcanic rock?

    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.

    + 4 more attachments

    Sobhi Nasir

     this texture is typical for undersaturated basalt with leucite (poly synthetitc twinning, low burefrengence|) and typical clinpyroxene laths, magnetite and olivine

  • Simon Spürgin added an answer:
    How to quantify graphite contents in rock powders?

    What is a useful method to quantify graphite contents in powdered rock samples? XRD does not work well due to the platy crystals and very strong preferred orientation, so I'm looking for an alternative method. Either by another analytical instrument, or by physical separation, or...

    Thanks, Simon

    Simon Spürgin

    Thanks to all your suggestions, showing very different methods to solve the issue!


  • Jayabalan Manickam added an answer:
    Are there any (online or offline) tutorials for GCDkit scripting in 'r' language?

    GCDkit is one of the most versatile packages for igneous petrology. Writing scripts in 'r' for GCDkit has a steep learning curve. Tutorials may help to facilitate learning with feedback.

    Jayabalan Manickam

    Dear Vojtech Janousek,

            Thank you for the information and links. 

  • Vojtech Janousek added an answer:
    Does anyone know the software-Minpet? Under the circumstance of Windows 8.1, it can't run, how do you deal with this situation?

    Minpet——( a software for Mineralogical and Petrological data processing system), it can run under the Windows system XP or Windows 7. However, it can't run under the circumstance of Windows 8.1. 

    Does anyone have the lastest version?

    Please contact with me, thank you!

    My e-mail is xiegen@cugb.edu.cn.

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