You can try in an EDAX without putting cover slip on thin section.

For plagioclase, you can try optical cathodoluminescence (CL). The An contents seem to be linked to the exact CL shade and the method is in non-destructive, enabling subsequent electron microprobe study, if necessary.

See e.g.

Janoušek, V., Braithwaite, C.J.R., Bowes, D.R. and Gerdes, A., 2004. Magma-mixing in the genesis of Hercynian calc-alkaline granitoids: an integrated petrographic and geochemical study of the Sázava intrusion, Central Bohemian Pluton, Czech Republic. Lithos, 78: 67-99.

But the books say the colors represents the chemical composition. is't it?

A tentative name of the mineral can be determined from the petrography, but the exact percentages of elements (K, Na, or any others) should be determined by quantitative mineral chemistry using the electron-probe micro-analyzer (EPMA)., or semi-quantitatevely using the EDX

Most reliable method would be using microprobe with wdx (wavelength dispersal). You can get precise composition of the spot selected. coverglass would have to be removed asnwell as adhesive on surface cleaned and surface should have glass finish

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..

Compositions of Plagioclase series from the thin section can be known but not accurately. EPMA has to be done for knowing the exact composition. Cleavage angle for example hornblende, pyroxene may help as well as birefrengence or 2v. We know some distinguishing chracateristics of many minerals , however, for exact composition EPMA is must.s

Happy to see good suggestions are pouring.

EPMA or QEMSCAN are non destructive methods where you can get both mineral and it's composition simultaneously

It is nice to see many good propositions for an identification method here. However, no single method applies well to all minerals due to their structure and sample observation geometry and representativity as well as sample monominerality/mineral intergrowth. In many cases the mineral lattice anisotropy is depending on the balance between two or more ions replacing each other in a continuous or semicontinuous composition series e.g. amphiboles, pyroxenes and feldspars. This stage of anisotropy can also be determined by very delicate optical crystallography method by measuring the double angle between the optical axis by Mallard method or by U-stage arrangement.

These methods are presently not widely used any more, but should be available for advanced users applying recent development in micro optical design. With these methods the composition is not possible to determine by themself, but by combining optical crystallography in advance polarizing microscope with energy dispersive methods, XRF, XRD and newly available UV-LIBS analytics and others, the results in many mineral series should appear good enough for Your thesis and publications.

Friends,

I have spent the greatest part of my life working upon the question as to how much more can be learned, beyond thin-section petrography, from applying a rigorous counting method of Becke-Line results while employing R. C. Emmons's double-variation, liquid-immersion techniques (Chapter 5, GSA Memoir 8, 1943; no Universal Stage needed in my work, where no attention is paid even to fragment orientation); with close controls over student-model petrographic microscope-stage illumination Wavelengths and Temperatures.

Since February my focus has been upon interpreting data from a Quantum-Mechanical perspective (thanks to gentle guidance from Dr. Vijay Chaudhry of India).

Chemical details remain elusive, but maps like those I obtain (for instance, please see the attached image) from intensive study of a single gabbro sample, for yet other suites of rocks, might -- together with similar work, on many different samples explored by teams via a variety of techniques (to include careful chemical analyses) -- help us to pin down just what is happening chemically at various locations of what I call the "Emmons Surface" of (Refractivity,Wavelength).

Sincerely, -Steve Langford-

A combination of methods such as XRF, XRD and spot analysis in EMPA, can be very helpful. In the case of Optical microscopy and EMPA, stained samples can add to the easier identification of minerals.

A combination of methods such as XRF, XRD and spot analysis in EMPA, can be very helpful. In the case of Optical microscopy and EMPA, stained samples can add to the easier identification of minerals.

You have got some good suggestions. My regards to all the contributors.

EPMA is obviously the best tool we have. But one cannot go to it for every sample. Besides, some of us do not have access to sophisticated instruments. I believe that one can still achieve a lot through application of classical petrography, combined with refractive index liquids and a refractometer; universal stage would be an added advantage. In thin sections, the An content of plagioclase can be well determined finding extinction angles on Carlsbad-albite twins combination or symmetrical extinction on albite twins in appropriately orientated grains. End-member compositions in plagioclase, Na-K feldspars and other simple solid solution systems such as common olivine, orthopyroxene, epidote, chlorite paragonite-muscovite, topaz, etc., can be determined fairly accurately with the help of refractive indices.

Best,

Qasim

Dear Mr. Sangsefidi:

There exists a classical booklet written in German with explanations in English and French which is dedicated to the determination of minerals in thin sections based upon their morphological and optical features with tables and diagrams illustrating the variation of optical properties in accordance with their chemical composition.

W.E. Tröger (1971) Optische Bestimmung der gesteinbildenden Minerale Teil 1 (Determination of rock-forming minerals based upon their optical features part 1 Tables for mineral determination).- E.Schweizerbartsche Verlagsbuchhandlung Stuttgart. 188 pages.

It is certainly no match for the EMPA but in case of using thin sections in the classical way it is still second to none for the applied geologist. It has diagrams showing the composition of feldspar s.s.s. and pyroxene s.s.s.

With kind regards

H.G.Dill

As others said above: EPMA, XRF, XRD are all options, as are QEMSCAN, Raman, and LA-ICPMS (as spot analyses, or for imaging whole slides). Each have strengths and weaknesses, that must be considered in light of your research questions, and of course instrument availability. For general petrology, but to a lesser degree for chemical variability within mineral groups, above mentioned Tröger (1971) is the classical and most cost-effective way. However, optical petrography involves a "steep learning curve" to say the least...

I am agree that EMPA is the beat method

the polished thin section with electron probe micro analysis can show edge effects like partitioning of ions by adjoining minerals, with potential to find temperature of formation.

I recommend Stephen's answer

Best Regards

H.G.Dill responded with a good recommendation for using optical only methods - I'd add to that the book by Wm Heinrich for good basic mineral id under the petrographic microscope.

Not everyone has access to EMPA or other instrumental methods, and even those of us who have often just want a quick determination under the microscope.

https://www.amazon.com/Microscopic-Identification-Minerals-heinrich/dp/007028055X

I agree with Lisa Fisher. For quick determination, Wm Heinrich and Kerr are good books. There are distinguishing optical optical properties of each mineral and these can be very effectively used. W .W . Moorehouse book can also be helpful in this regard.

A treasure of information on a very large number of non-opaque minerals is given in:

Wm. Revell Phillips & Dana T. Griffen, Optical Mineralogy, the Nonopaque Minerals. (WH Freeman & Co). The Indian editions of this book (2004 latest reprint) sells for peanuts!

Is there a good reference that teaches how to collect statistically significant data sets of parameters measured during routine, production-line, optical-mineralogy studies? -Steve-

I recommend Stephen's answer

Thanks again, Osama Rahil! :-)

Yesterday I submitted a comprehensive paper on "all this". I look forward to being able to say more ASAP. -Steve-

For composition, you need EPMA

Thank you, Kayode Amuda! Your guidance has led me to "There are however, many mineralogical studies where there are considerable benefits to be derived from using an EPMA equipped with WD spectrometers" (from

https://www.researchgate.net/publication/229172111_Mineral_characterisation_by_EPMA_mapping ).

The way things are going, I guess that such instruments may already be in play on Mars and soon might become so portable as to be of use to field Geologists. Ultimately, it would be really educational to be able to plot EPMA-WD and such results as overlays to maps showing how much mass is found at various Refractive Indices (RIs, unitless) and Wavelengths ( λ , nm), for each sample. Cross-discipline, cooperative studies of identical Standard samples might go far in further advancing our capabilities to comprehend critically-related aspects of Material Sciences, such as how various Rock and Mineral Chemistries relate to displayed RIs. -Steve-

Yes

It is possible. There are optical tables that permit to You to determine, in case of solid solution, the amount of a compound.

For example, in plagioclase, you can determine the amount of Ab vs. An (+- 2%) using a combination of Simmetric extintion + Relief + Optical Sign.

In Augite-Aegirine series, you can determine the Aeg (or Acmite) compound through the determination of the C^Z (elongation) + Optical Sign + 2V angle.

It is the base of petrogrphy.

Cheers

Federico

Friends,

With what degree of statistical significance, related to describing the solid-solution details of a given mineral expressed by a whole-rock sample, is such work typically done?

Thanks, -Steve-

we are talking of Thin Section observation at polarized microscopy.

It is optical determination, on single mineral in thin section.

Felix Chayes generated voluminous publications regarding statistical approaches to thin-section work. However, thin-section work fails in regions of extreme fine grain, I believe. Even in course-grained thin-section work, the most-common rock-forming minerals, plagioclase feldspars, are typically zoned compositionally, making "IDs" from such as a single 2V measurement effectively useless in terms of describing the compositional spread of plagioclase phases in the sample. Who is providing even elementary statistics of mean and standard deviation of composition, from optical mineralogy work, please?

Thanks, -Steve-

Dear Stephen, there are voluminous tables and paper that describes how to determine a mineral species in thin section.

Just to cite one of the most famous: Tröger,W.E. Optical Determination of Rock-forming Minerals—Part 1 Determinative Tables; English Edition of

the Fourth German Edition; Bambauer, H.U., Taborzsky, F., Trochim, H.D., Eds.; E. Schweizerbart’sche Verlagsbuchhandlung (Nägele u. Obermiller): Stuttgart, Germany, 1979.

Second, in all bachelor degrees in Geology and Mineralogy (in Italy) there are courses of petrography and mineralogy where it is teached on how to determine with polarized microscopy the composition of a mineral.

The mineral could be very little (such as groundmass in volcanic rocks) but with a microscope equipped with 60x or 100x lens (Nikon or Leica educational microscopes for example) it is possible to determine good parameter down to crystal of 300 microns.

Concerning the efficient of this kind of approach

Just think the international normative regarding asbestos (i.e. fibers) says that one of the four methods accepted for Asbestos definition and classification is Polarizing microscopy.

Article Naturally Occurring Asbestos (NOA) in Granitoid Rocks, A Cas...

This paper from me, it has been published now and show how the Pol.Mic is a very efficient method.

Our classification using optical parameters matched totally the EMPA analyses.

Best.

F

Stephen is raising interesting and important questions, but we have to keep in mind the need of the study. If the purpose is to identify common rock-forming silicate minerals for the sake of petrographic classification of the rocks, an ordinary polarizing microscope is enough unless the rocks are too fine-grained or highly altered. Additional help can be gained from determination of Refractive Indices (a method I found very useful, but not very popular nowadays). As Federico said, there are many books on optical mineralogy and petrography that can be used for support. But if one needs additional details on the composition and structure of the minerals in the rock, one obviously has to go to instruments such as XRD, SEM, TEM, EPMA, etc.

Lastly, I have always enjoyed aesthetically the beauty of silicate minerals through the tube of the polarizing microscope.

Furthermore I would like to remember that the question says:

How mineral can be determined in thin section.

If it is a normal section, not a polished one, only pol.mic. will work

I appreciate your enthusiasm and expertise, Federico Lucci. I keep copies of Tröger close at hand, and I own two petrographic microscopes, one of which I bought from famed US Dept. Agriculture microscopist Francis T. Jones. It is much like this one: https://tinyurl.com/y9xoqdkv and is for sale. Serious inquiries regarding its possible purchase are welcome.

My other scope is a Unitron MPS https://tinyurl.com/ydhng9hs, which I modified for close temperature and wavelength controls, in order to be able to apply the methodology of R. C. Emmons

Emmons, R. C., 1943. The Universal Stage (With five axes of rotation).

Geol. Soc. Am. Memoir 8. Judd & Detweiller; Washington, D. C.; 205 pp.,

Plates 8 through 13 in jacket pocket. Ch. 5. Double variation procedure for

refractive index determination, pp. 55 – 101. http://memoirs.gsapubs.org/content/8

A copy of that Chapter 5 http://tinyurl.com/oz98vpu has been provided for your convenience and mine, through the great kindness of GSA representatives Jeanette Hammann and Geoff Feiss.

My work ignores the Universal Stage aspects of that chapter and was inspired by Gerald P. “Gerry” Brophy, who taught in 1961 that geologists were ignoring Refractive Index to their own disadvantage. When I asked Dr. Brophy whether RI work might be done to good advantage without bringing any fragment to a known optical orientation, he responded that a statistical approach to such data might prove to be useful, and I promised to investigate that. My initial work is reported in

Langford, S. A., 1972. Statistical method in optical crystallography:

Technique and application to rock forming minerals.

Univ. Hawaii dissertation, 185 pp.

https://scholarspace.manoa.hawaii.edu/bitstream/10125/11643/1/uhm_phd_7315944_r.pdf

Later, I focused upon a single sample of gabbro collected from West Maui, Hawaii and passed about 1cc. of it through a 400-mesh (0.0381mm.) screen to create the powder studied since 23 October 1977. I congratulate you on the successes you have had matching EMPA analyses. Though my petrography was once good enough at one point to build a spindle stage just so I could actually see the optic figure of a sillimanite spicule [try *that*, just for fun! ;-) ], I was never satisfied that thin-section studies provided a *thoroughly general* approach that could be applied to *any* specimen. I note in passing that the fineness of my powdered gabbro is an order of magnitude less than your mentioned 300 microns. I must also note in passing:

McCrone, W. C. and Anna Teetsov, 1968.

Measuring the refractive indices of subnanogram particles.

The Particle Analyst, v. 1, no. 18, Sept. 20, 153 - 160.

McCrone, W. C., and A. Teetsov, 1969.

Measuring the refractive indices of subnanogram particles.

The Microscope, v. 17, no. 1, pp. 83 - 90.

My recent work has been intended to discover how much we might learn about rocks from RI data alone. I have intensively studied one whole-rock powder. My attempts to publish have been repeatedly rejected, though my most-recent manuscript is now with a publisher who has not yet kicked it back at me.

Gordon A. Macdonald described the plagioclase in a sample from the same plug my sample came from, as follows: “The plagioclase crystals contain cores of calcic to intermediate labradorite surrounded by strongly zoned shells in which the composition grades to andesine at the outside.” My work shows that the entire range of plagioclase RIs is expressed.

I have no argument with good thin-section work! I have oriented thin sections of the 67 samples that I collected from Maui. But my curiosity led me to question how trustworthy my own thin-section results were. Too often, when I turned away from the scope and moved to a randomly achieved position, I landed on grain boundaries or on things too small to study for the purpose at hand. And none of the thin section work gave me any very useful measure of RI … which I was taught is the most-important parameter of all to study when identifying a mineral.

I, too, “… have always enjoyed aesthetically the beauty of silicate minerals through the tube of the polarizing microscope”, M. Qasim Jan. :-) I once gave a lecture in a movie theater, for which I adapted a Carousel projector to permit me to rotate a thin section between cross-polarized plastic strips, so that the effect could be appreciated by my students and guests. And by no means do I mean to propose that everything one wants to learn about the compositional variability of mineral solid solutions in any given sample can be learned from RI studies alone! I would be the first to suggest that more teamwork should be given to a suite of petrographic standard samples, employing all techniques that can add to our comprehension of fundamental interrelationships among geochemistries and the most-important factors related to them.

Anyway, my adventure has been intriguing and has led me to a better appreciation of such related topics as the Law of Gladstone and Dale, e=mc^2, and quantum mechanics (not a topic I claim to have mastered).

I hope to be able to share much more via the intended publication of my most-recent manuscript, more of which I dare not reveal in this informal venue … at least at this time. But some readers might appreciate sharing my winning entry in the 2017 https://www.lpl.arizona.edu/art/ show and contest; please see it in the Data Art category, at https://www.lpl.arizona.edu/art/2017.

Thanks to each of you who have contributed to this interesting thread.

Sincerely, -Steve-

Well, Federico Lucci, given your “Furthermore I would like to remember that the question says: How mineral can be determined in thin section. If it is a normal section, not a polished one, only pol.mic. will work”, I must say that aphanitic samples eluded my own successful T.S. study. RI studies of rock powders can generate details related to chemical variabilities over complete ranges of mineral phases, as well as means, standard deviations, and other related statistics, for mineral separates. So at times my answer to the original question that you rightfully revive must be: Sometimes a mineral can not be identified from thin-section work alone. Rarely can comprehensive details related to phase ranges of mineral solid solutions be gleaned from thin-section work. That you have produced from thin-section work alone results that “matched totally” EMPA analyses is indeed impressive to me. I doubt that you could do so with finely aphanitic samples, though.

Dr. Brophy taught that geochemists were ignoring the work of optical mineralogists, because they were not providing data that could be closely explanatory of related geochemical results. Perhaps you can tell me how much has changed in that regard, since 1961. :-)

Sincerely, -Steve-

i am also interested in the answer to enable me do a modal classification of minerals in the thin sections of the rocks i am studying.

Edwin, do you have the ability to take a course in optical mineralogy? If not, there are many good textbooks available for self-study. Depending on your study area and the complexity of the rocks there - you may be able to learn the basic minerals that occur in your samples without too much trouble. As far as the modal analysis, you can do a point count, or you can use the black and white charts that show % of minerals to aid you in estimating the modes. If you want more detail, please ask.

Dear Edwin Mbiimbe, you may like to check out our overview of the topic in:

Janoušek V, Navrátil T, Trubač J, Strnad L, Laufek F, Minařík L (2014) Distribution of elements among minerals of a single (muscovite-) biotite granite sample - an optimal approach and general implications. Geol Carpath 65: 257–271

http://www.geologicacarpathica.com/browse-journal/volumes/65-4/article-726/

I trust that this helps, Vojtech

Dear Colleagues,

in the classical way I can only refer to the book issued by Tröger 1971 "Optical determination of rock-forming minerals " volume I and II (volume I has been issued in German, English and French language). There are numerous data and diagrams which should be of assistance for your studies. If you have thin (thick ) sections uncovered with a glas you can ship your rock slap to a lab for EMPA. It will be the up-to-date method currently.

Kind regards

H.G.Dill

The first hand identification of the rock forming minerals is done based on their overall optical properties in plane polarised light and crossed nicols (Ref. Introduction to rock forming minerals by Deer, Howie, Zussman, 2nd Edition).

For further identification of sub species, determination of pleochroic scheme can be useful to certain extent eg. for colored minerals like some amphiboles, sodic pyroxene), extinction angle (plagioclase feldspar), optic axial angle (eg. Sanidine and orthoclase, both monoclinic K-feldspars), refractive Index (eg. for garnet species), sign of elongation (sillimanite and andalusite if confirmation is required).

Staining techniques are of immense utility for first hand identification of feldspars (untwinned and or altered) , carbonate minerals like calcite, ferroan calcite, dolomite and ferroan dolomite) and some feldspathoids. Nepheline can be confirmed by its uniaxial negative optic sign and also by staining with methylene blue.

Sometimes a combination of very basic aspects like low relief and absence of cleavage (quartz), high relief, absence of cleavage and isotropic (garnet), high relief, absence of cleavage, anisotropic and birifringence (olivine), high negative relief and relative refractive index (fluorite), magnetic susceptibility (magnetite or even martitised magnetite).

Fundamental knowledge of rock mineral association can also be helpful

eg. igneous rocks; the common rock forming minerals that can be associated with ultramafic, mafic, intermediate and felsic rocks. Occurrence of Na plagioclase as an alkali feldspar, as an albite or oligoclase with felsic rocks, occurrence of oligoclase / andesine with intermediate rocks, occurrence of labradorite and bytownite with mafic rocks.

However despite our best efforts sometimes we may not be able to definitely identify all the minerals in the thin sections based on optical properties. In such cases, the thin cum polished sections can be used for EPMA or SEM studies. EPMA can provide information only on the mineral chemistry. For determination of FeO and Fe2O3 particularly for Fe bearing minerals in alkaline rocks, wet chemical analyses (digested mineral seperate) involving titration is essential.

XRD studies provide information on the internal structure of the minerals.

Chayes, Felix, 1948. Statistical Petrography section, reprint from Carnegie Inst. Wash. Year Book no. 47, issued December 1948, no. 1108, pp. 27 - 52. See esp. p. 45.

Chayes, Felix, 1949. On ratio correlation in petrography; J. Geol., v. 57, no. 3, pp. 239 - 354.

Chayes, Felix, 1952. Relations between composition and indices of refraction in natural plagioclases; Bowen Volume, Am. J. Sci., v. 1, pp. 85 - 105.

Chayes, Felix, 1954. A test of the revised determinative chart for plagioclase; Am. J. Sci., v. 252, pp. 172 - 180.

Chayes, Felix, 1956. Petrographic Modal Analysis; John Wiley & Sons, New York; Chapman Hall, London; 113 pp.

Chayes, Felix, 1960. On correlation between variables of constant sum. J. Geophys. Res., v. 65, no. 12, 4185 - 4193.

Chayes, Felix, 1962. Numerical correlation and petrographic variation. J. Geol., v. 70, pp. 440 - 452.

Chayes, Felix, 1967. Modal compositions of U. S. G. S. reference sample G-2. Geochim. Cosmochim. Acta, v. 13, pp. 463 - 464.

Chayes, Felix, 1970. On deciding whether trend surfaces of progressively higher order are meaningful. Geol. Soc Am. Bull., v. 81, pp. 1273 - 1278.

Chayes, Felix, 1971. Ratio Correlation. Univ. Chicago Press, Chicago and London, 99 pp.

Chayes, Felix, 1975. On the need, design, and prospect for an electronic information system serving igneous petrology. Math. Geol., v. 7, nos. 5/6, pp. 363 - 371.

Chayes, Felix, 1977. On ways of making information system software available. Papers from the Geophysical Laboratory, Carnegie Institution of Washington, no. 1715, Permagon Press, v. 3, no. 3, pp. 449 - 452.

Chayes, Felix, 1977, Sampling variation of principal components. Math. Geol., v. 9, no. 5, pp. 497 - 506.

Chayes, Felix, 1977. Version NTRM2 of system RKNFSYS. Carnegie Inst. Wash, Geophys. Lab., unpublished manuscript, 76 pp.

Chayes, Felix, 1978. Status of the project for development of a world data base for igneous petrology. In Carnegie Inst. Wash. Geophys. Year Book 77, issued December 1978, no. 1755, p, 902.

Chayes, Felix, 1980. Defining rock types by composition ranges. Chemical Geology, v, 30, pp, 309 - 315.

Chayes, Felix, and W. Kruskal, 1966. An approximate statistical test for correlations between proportions. J. Geol., v. 74, pp. 692 - 702.

Chayes, Felix, and Jürgen Trochimczyk, 1978. An effect of closure on the structure of principal components. Math. Geol., v. 10, no. 4, pp. 323 - 333.

Chayes, Felix, and J. Trochimczyk, 1978. The effect of the principal component transformation on closure correlation. in Carnegie Inst. Wash. Geophys. Year Book 77, issued December 1978, no. 1755, pd. 898 - 900.

- - - - -

However, I do not consider myself to be an expert in thin-section analysis.

My own work to map refractive indices displayed by mineral-separate and whole-rock powders has been aimed at bringing the double-variation, liquid-immersion approach [best outlined by

Chapter 5 http://tinyurl.com/oz98vpu (Double variation procedure for refractive index determination, pp. 55 – 101) of

Emmons, R. C., 1943. The Universal Stage (With five axes of rotation). Geol. Soc. Am. Memoir 8. Judd & Detweiller; Washington, D. C.; 205 pp., Plates 8 through 13 in jacket pocket.]

to the same level of statistical sophistication as Chayes brought to thin-section work.

I hope this helps.

I'm attaching some recent art produced during some of my latest science.

Sincerely -Steve-

The anorthite content of plagioclse can be determined by Michael Levy method by choosing appropriate grain to measure extinction angle using polarising microscope under crossed Nicols.

When you see rock mineral association for igneous rocks, Na plagioclse i.e. albite to oligoclase is associated with felsic rocks, andesine with intermediate and alkaline rocks and Labradorite to bytownite with mafic rocks. Anorthite content of more than 90 can be seen in CA plagioclse associated with anorthosites. Bytownite to anorthite i.e. Ca between 70 to 90 or can be present in plagioclse associated with gabbroic anorthosites or troctolites.

Feldspar mineral chemistry can be obtained with EPMA and the end members can be calculated using cation data.

Regarding oyroxene Na pyroxene can be aegerine augite or aegerine that are associated with alkaline rocks in which Na is more than Al i.e. peralkaline rocks. Aegerine, a Na ferric Fe rich clinopyroxene is strongly pleochroic in shades of yellow and lemon green and has low extinction angle. It is usually associated with alkali feldspar in alkaline rocks.

However, determination of FeO and Fe2O3 by titration will give authentic information for petrogenesis of aegerine bearing rock, since EPMA cannot quantify both the Fe oxidation states. ( For details please consult any Edition of Deer, Howie, Zuessman book dealing with An Introduction to Rock Forming minerals)

V. V. Sesha Sai, what you say is true! But have you considered how to make your work statistically significant? I found the complete range of Plagioclases and more, via comprehensive liquid-immersion work. I dare say that my results are more comprehensive than any that might have been obtained by Felix Chayes himself. Please see the attached image.

With all best wishes for your continuing successes; respectfully;

-Steve- [email protected] ... https://tinyurl.com/to8tsbt

RAW DATA & Explanations .csv.pdf:

https://www.dropbox.com/s/tk1zqko1ctsasxo/RAW%20DATA%20%26%20Explanations%20.csv%20.pdf?dl=0

Thank you very much Dr.Langford. Excellent work. I am basically a field worker who tries to understand the mineralogy and textures of the rocks in thin sections. Experimental petrology is dream to me. I understand the significance of the contribution made by experimental petrology in petrogenetic studies. Even today there is lot of scope. Once again thank you and congratulations

Dear V. V. Sesha Sai, Thank you for your kind response! :-) As a minor point, merely to clarify my own perspective ... I believe that the word "petrology" has been hijacked! :-) I know that it should mean nothing more than the study of rocks, but it has been used so much to focus upon relational geochemistries, phase diagrams, and so many theoretical aspects as to warrant a clear distinction between "petrology" and "petrography", the latter of which I reserve to descriptive work, as in "what do we have, here?". My personal choice has been to try to be able better to say what these things we call minerals and rocks are, before daring to delve into the theoretical work related to how they came to be.

Just as I find a problem with petrography versus petrology, I find the same with mineralogy and what I would prefer to call mineralography. I am not sure that I have ever seen the latter written anywhere! But "Optical Mineralogists" might better be called "Optical Mineralographers"; at least from my own perspective. ;-)

One goes with the flow: "Go along to get along". ;-)

I am reminded of the time I told my Dissertation Chairman, Dr. Gordon A. Macdonald -- famed for his beautiful rock descriptions -- that "Hawaiite" is misspelled! For all I know, he named that type. This was before people started spelling the state name "Hawai'i". I was thinking that the rock name should actually be "Hawaiiite"! Dr. Macdonald smiled and said he'd leave that one to me. Well, maybe it should be "Hawai'iite". But don't tell anybody that I said so. ;-)

Thank you for recognizing the importance of my work. Now, how do we automate data collection, analysis, and display? ;-) I've been asking that question for at least 40 years.

With all best wishes for your continuing successes; respectfully;

-Steve- [email protected] ... https://tinyurl.com/to8tsbt

RAW DATA & Explanations .csv.pdf:

https://www.dropbox.com/s/tk1zqko1ctsasxo/RAW%20DATA%20%26%20Explanations%20.csv%20.pdf?dl=0

EPMA will help quantify the variations in plagioclase family end members.

To toot my own horn, 2 of my articles published today may interest petrographers:

http://www.cjpas.net/wp-content/uploads/pdfs/15/1/2%20Langford%205133-5140.pdf

and

http://www.cjpas.net/wp-content/uploads/pdfs/15/1/5%20Langford%205169-5178%20.pdf

published in this issue

http://www.cjpas.net/current-issue/

of The Canadian Journal of Pure and Applied Sciences (CJPAS).

Respectfully, -Steve-

[email protected] ... https://tinyurl.com/to8tsbt

https://www.researchgate.net/publication/346020796_GUIDE_READ_ME_FIRST

RAW DATA & Explanations .csv.pdf:

https://www.dropbox.com/s/tk1zqko1ctsasxo/RAW%20DATA%20%26%20Explanations%20.csv%20.pdf

Sometime the pleochroism may be indicator of chemical composition. For example in the chlorites