X-Rays of Oriented Aggregates

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Clay Mineral Identification Flow Diagram X-rays of Oriented Aggregates Randomly-oriented Heated to 400oC Heated to 550oC Electron micrograph aggregate mount of clay Treated with ethylene glycol if required fraction (<2 m) Air Dried at least ½ hour at least ½ hour Results Expands to 31-32 with Regularly interstratified chlorite- ~29 May disappear or Increases in intensity rational sequence of give 24 spacing of 24 spacing montmorillonite or chlorite- higher orders vermiculite (corrensite) Expands May give irrational sequences May give irrational Randomly interstratified chlorite- but gives irrational sequence -- may show increase in intensity sequence montmorillonite Peaks may be broad of 12-14 peak ~14 No change No change Increases in intensity 060 near 1.54 Chlorite 060 near 1.50 Dioctahedral chlorite No change or No change or slight Collapses to ~10 060 near 1.54 slight increase additional collapse Vermiculite Additional collapses Slight collapse to ~12 to ~11 060 near 1.50 Dioctahedral vermiculite No change or slight Expands to 17 Collapses to ~10 060 near 1.50 additional collapse Montmorillonite Collapses to ~10 No change or slight 060 near 1.52 with very weak 5 peak additional collapse Nontronite Trioctahedral montmorillonite 060 near 1.54 or vermiculite >10-14 No change - Regularly interstratified Rational sequence of Collapses to ~10 Collapses to 10 060 near 1.54 higher orders. illite-vermiculite No change or slight Regularly interstratified No change 060 near 1.54 increase in intensity illite-chlorite No change - Randomly interstratified Collapses to ~10 Collapses to 10 060 near 1.54 Irrational sequence illite-vermiculite No change or slight Randomly interstratified No change 060 near 1.54 increase in intensity illite-chlorite Expands to Interstratified Collapses to ~10 Collapses to 10 060 near 1.50 higher spacing illite-montmorillonite 060 near 1.54 Interstratified trioctahedral illite-montmorillonite Interstratified dioctahedral No change Slight collapse Further collapse 060 near 1.50 illite-vermiculite Destroyed or reduced Check hkl’s 12-12.5 No change Destroyed Fibrous morphology Sepiolite in intensity against standard Destroyed - - may Check hkl’s 10.5 No change survive slightly at Destroyed Fibrous morphology Palygorskite against standard lower temperature 060 between Illite (and/or mica), ~10 Symmetrical No change No change No change 1.51 - 1.52 muscovitic, 5 peak very various polymorphs 060 between Glauconite or 1.51 - 1.52 Celadonite 5 peak very (Roscoelite if V bearing) 060 near 1.54 Biotite various polymorphs Interstratified Unsymmetrical or No change or illite-montmorillonite or 060 variable slight shift either way slight sharpening illite-vermiculite (Illite) Expands to ~11 Collapses to ~7 Destroyed Tubular morphology 060 near 1.49 Endellite Check hkl’s 7 No change No change No change Fibrous morphology Chrysotile against standard Check hkl’s Platy morphology Antigorite against standard 060 near 1.49 Disordered kaolinite Destroyed Platy morphology hk bands present (Fireclay) moderately broad 001’s 060 near 1.54 Chlorite Dioctahedral 060 near 1.50 Chlorite Kaolinite Hexagonal morphology hkl’s resolved Dickite Nacrite Increase in spacing Collapses to 7 Destroyed Tubular morphology 060 near 1.49 Halloysite or no change hk bands present.

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M]NIJRALOGICAL NOTI'S 229 Talr,e 1. Cnrutcet Conpostrron ol Wnolvolrrtn lnon Vanrous Souncos CaO 38 38 38.46 38 83 38.36 38 23 C:O: 49 28 49.65 49.38 50.28 48.69 HrO 12.34 72 74 123l 11.36 Not Determined 1. Ca(C:Oa).HrO 2. Pchery', Bohemia 3. Briix, Bohemia 4. Maikop, Caucasus 5. Milan, Ohio Note: Analyses 2,3 and 4 from Palache et ol. (195L). This find is of interest for the following reasons: 1. It is the first reported in easternUnited States.2. It is the first of any sizablequantity in the United States.3. It is found in older rocks than previous finds. 4. The location is readilv accessibleto interested petrologists. We are glad to acknowledgethe help of Mr. Owen Keim who per- formed the chemicalanalysis and Mr. C. R. Tipton, Jr. who made this work possibie,both of whom werethe authors' associatesat the BasicIn- corporated ResearchCenter. Of course,special thanks and recognition must go to Mr. ClarenceRaver rvhosupplied us with the samples. RrlBnrNcos Guon, A. J., 3rd, E. J. YouNc, V. C KnNNrov aNn L. B Rrr.r:v (1960) Wheu,ellite and celestitefrom a fault opening in San Juan County, IJtah- Am. Mineral.45,1257-1265. Per.ecun, C, H. BnnlreN aNo C FnoNou. (1951) Danos' SystemoJ Mineralogy, Vol. II, 7th ed., John lViley and Sons,Inc., Nelr' York. Pocon.r, W T eNo J. H. Krnn (1954) Whewellite from a septarian iimestone concretion in marine shalenear llavre, Montana Am. Mineral.Jg,208-214. THE AMERICAN MINERALOGIST,VOL 51, JANUARY_FEBRUARY,1966 LACLTSTI{INE GLAUCONITIC MICA FROM PI,UVIAL LAKE MOUND.
17. Clay Mineralogy of Deep-Sea Sediments in the Northwestern Pacific, Dsdp, Leg 20

17. CLAY MINERALOGY OF DEEP-SEA SEDIMENTS IN THE NORTHWESTERN PACIFIC, DSDP, LEG 20 Hakuyu Okada and Katsutoshi Tomita, Department of Geology, Kagoshima University, Kagoshima 890, Japan INTRODUCTION intensity of montmorillonite can be obtained by sub- tracting the (001) reflection intensity of chlorite from the Clay mineral study of samples collected during Leg 20 of preheating or pretreating reflection intensity at 15 Å. the Deep Sea Drilling Project in the western north Pacific In a specimen with coexisting kaolinite and chlorite, was carried out mainly by means of X-ray diffraction their overlapping reflections make it difficult to determine analyses. Emphasis was placed on determining vertical quantitatively these mineral compositions. For such speci- changes in mineral composition of sediments at each site. mens Wada's method (Wada, 1961) and heat treatment Results of the semiquantitative and quantitative deter- were adopted. minations of mineral compositions of analyzed samples are The following shows examples of the determination of shown in Tables 1, 2, 3, 5, and 7. The mineral suites some intensity ratios of reflections of clay minerals. presented here show some unusual characters as discussed below. The influence of burial diagenesis is also evidenced Case 1 in the vertical distribution of some authigenic minerals. Montmorillonite (two layers of water molecules between These results may contribute to a better understanding silicate layers)—kaolinite mixture. of deep-sea sedimentation on the northwestern Pacific This is the situation in which samples contain both plate. montmorillonite and kaolinite. The first-order basal reflec- tions of these minerals do not overlap. When the (002) ANALYTICAL PROCEDURES reflection of montmorillonite, which appears at about 7 Å, Each sample was dried in air, and X-ray diffraction is absent or negligible, the intensity ratio is easily obtained.
Download PDF About Minerals Sorted by Mineral Name

MINERALS SORTED BY NAME Here is an alphabetical list of minerals discussed on this site. More information on and photographs of these minerals in Kentucky is available in the book “Rocks and Minerals of Kentucky” (Anderson, 1994). APATITE Crystal system: hexagonal. Fracture: conchoidal. Color: red, brown, white. Hardness: 5.0. Luster: opaque or semitransparent. Specific gravity: 3.1. Apatite, also called cellophane, occurs in peridotites in eastern and western Kentucky. A microcrystalline variety of collophane found in northern Woodford County is dark reddish brown, porous, and occurs in phosphatic beds, lenses, and nodules in the Tanglewood Member of the Lexington Limestone. Some fossils in the Tanglewood Member are coated with phosphate. Beds are generally very thin, but occasionally several feet thick. The Woodford County phosphate beds were mined during the early 1900s near Wallace, Ky. BARITE Crystal system: orthorhombic. Cleavage: often in groups of platy or tabular crystals. Color: usually white, but may be light shades of blue, brown, yellow, or red. Hardness: 3.0 to 3.5. Streak: white. Luster: vitreous to pearly. Specific gravity: 4.5. Tenacity: brittle. Uses: in heavy muds in oil-well drilling, to increase brilliance in the glass-making industry, as filler for paper, cosmetics, textiles, linoleum, rubber goods, paints. Barite generally occurs in a white massive variety (often appearing earthy when weathered), although some clear to bluish, bladed barite crystals have been observed in several vein deposits in central Kentucky, and commonly occurs as a solid solution series with celestite where barium and strontium can substitute for each other. Various nodular zones have been observed in Silurian–Devonian rocks in east-central Kentucky.
High Dose Dosimetry Using Antigorite-Teflon Composite

2011 International Nuclear Atlantic Conference - INAC 2011 Belo Horizonte,MG, Brazil, October 24-28, 2011 ASSOCIAÇÃO BRASILEIRA DE ENERGIA NUCLEAR - ABEN ISBN: 978-85-99141-04-5 HIGH DOSE DOSIMETRY USING ANTIGORITE-TEFLON COMPOSITE René R. Rocca 1, Sonia H. Tatumi 2 and Shigueo Watanabe 1 1 Instituto de Física Universidade de São Paulo Rua do Matão 187 – Travessa R. 05508-090 Butantã, SP [email protected] – [email protected] 2 Faculdade de Tecnologia de São Paulo CEETESP Pça. Cel. Fernando Prestes - Bom retiro, 30 01124-060 São Paulo, SP [email protected] ABSTRACT Pellets of antigorite crystals (Mg 3-x [Si 2O5] (OH) 4-2x ) and teflon powder were obtained in order to investigate the thermoluminescence (TL) dosimetric characteristics. ICP analysis was performed showing the presence of 0.25 mol% of Fe 2O3, 0.07 mol% of Al 2O3 and 0.006 mol% of MnO impurities. These pellets show two prominent TL peaks at 150 oC and another broad one at 250 oC observed in samples previously irradiated with gamma-rays from 60 Co source. The 150 oC peak increased up to 2 kGy and after this dose the intensity reaches a maximum then decreases gradually. However the 250 oC peak increased up even with a dose of 172 kGy. A good reproducibility of TL results was obtained showing that these pellets can be used for high dose measurements. An excellent theoretical fit using second order kinects model [10] was obtained for all the peaks; however the theoretical deconvolution [4] showed the presence of two additional peaks at 206 and 316 oC.
Roscoelite K(V ; Al; Mg)2Alsi3o10(OH)2 C 2001 Mineral Data Publishing, Version 1.2 ° Crystal Data: Monoclinic

3+ Roscoelite K(V ; Al; Mg)2AlSi3O10(OH)2 c 2001 Mineral Data Publishing, version 1.2 ° Crystal Data: Monoclinic. Point Group: 2=m: As minute scales, in druses, rosettes, or fan-shaped groups; ¯brous and in felted aggregates; as impregnations, massive. Physical Properties: Cleavage: Perfect on 001 . Hardness = Soft. D(meas.) = 2.92{2.94 D(calc.) = [2.89] f g Optical Properties: Transparent to translucent. Color: Dark clove-brown, greenish brown to dark greenish brown. Luster: Pearly. Optical Class: Biaxial ({). Pleochroism: X = green-brown; Y = Z = olive-green. ® = 1.59{1.610 ¯ = 1.63{1.685 ° = 1.64{1.704 2V(meas.) = 24.5±{39.5± Cell Data: Space Group: C2=c: a = 5.26 b = 9.09 c = 10.25 ¯ = 101:0± Z = 2 X-ray Powder Pattern: Paradox Valley, Colorado, USA. 10.0 (100), 4.54 (80), 3.35 (80), 2.60 (80), 1.52 (60), 3.66 (50), 3.11 (50) Chemistry: (1) SiO2 47.82 Al2O3 12.60 V2O5 19.94 FeO 3.30 MgO 2.43 CaO trace Na2O 0.33 K2O 8.03 + H2O 5.13 Total 99.58 (1) Stuckslager mine, California, USA. Polymorphism & Series: Forms a series with muscovite; 1M polytype. Mineral Group: Mica group. Occurrence: An early-stage gangue mineral in low-temperature epithermal Au-Ag-Te deposits; from the oxidized portions of low-temperature sedimentary U-V ores. Association: Quartz, pyrite, carbonates, °uorite, gold (Au-Ag-Te mineral association); corvusite, hewettite, carnotite, tyuyamunite (U-V mineral association). Distribution: In the USA, from the Stuckslager mine, Lotus, El Dorado Co., California; in Colorado, from Cripple Creek, Teller Co., La Plata district, La Plata Co., Magnolia district, Boulder Co., the Gateway district, Mesa Co., in the Uravan and Paradox, Bull Canyon, and Slick Rock districts, in Montrose, San Miguel, and Dolores Cos.
Washington State Minerals Checklist

Division of Geology and Earth Resources MS 47007; Olympia, WA 98504-7007 Washington State 360-902-1450; 360-902-1785 fax E-mail: [email protected] Website: http://www.dnr.wa.gov/geology Minerals Checklist Note: Mineral names in parentheses are the preferred species names. Compiled by Raymond Lasmanis o Acanthite o Arsenopalladinite o Bustamite o Clinohumite o Enstatite o Harmotome o Actinolite o Arsenopyrite o Bytownite o Clinoptilolite o Epidesmine (Stilbite) o Hastingsite o Adularia o Arsenosulvanite (Plagioclase) o Clinozoisite o Epidote o Hausmannite (Orthoclase) o Arsenpolybasite o Cairngorm (Quartz) o Cobaltite o Epistilbite o Hedenbergite o Aegirine o Astrophyllite o Calamine o Cochromite o Epsomite o Hedleyite o Aenigmatite o Atacamite (Hemimorphite) o Coffinite o Erionite o Hematite o Aeschynite o Atokite o Calaverite o Columbite o Erythrite o Hemimorphite o Agardite-Y o Augite o Calciohilairite (Ferrocolumbite) o Euchroite o Hercynite o Agate (Quartz) o Aurostibite o Calcite, see also o Conichalcite o Euxenite o Hessite o Aguilarite o Austinite Manganocalcite o Connellite o Euxenite-Y o Heulandite o Aktashite o Onyx o Copiapite o o Autunite o Fairchildite Hexahydrite o Alabandite o Caledonite o Copper o o Awaruite o Famatinite Hibschite o Albite o Cancrinite o Copper-zinc o o Axinite group o Fayalite Hillebrandite o Algodonite o Carnelian (Quartz) o Coquandite o o Azurite o Feldspar group Hisingerite o Allanite o Cassiterite o Cordierite o o Barite o Ferberite Hongshiite o Allanite-Ce o Catapleiite o Corrensite o o Bastnäsite
First-Principles Modeling of the Infrared Spectrum of Antigorite

Eur. J. Mineral., 33, 389–400, 2021 https://doi.org/10.5194/ejm-33-389-2021 © Author(s) 2021. This work is distributed under the Creative Commons Attribution 4.0 License. First-principles modeling of the infrared spectrum of antigorite Etienne Balan1, Emmanuel Fritsch1,2, Guillaume Radtke1, Lorenzo Paulatto1, Farid Juillot1,2, and Sabine Petit3 1Sorbonne Université, CNRS, MNHN, Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie (IMPMC), 4 place Jussieu, 75252 Paris CEDEX 05, France 2Institut de Recherche pour le Développement (IRD), Centre de Nouméa, 101 Promenade Roger Laroque, Anse Vata, 98848 Nouméa, New Caledonia 3Institut de Chimie des Milieux et Matériaux de Poitiers (IC2MP), CNRS UMR 7285, Université de Poitiers, 6 rue Michel Brunet, 86073, Poitiers CEDEX 9, France Correspondence: Etienne Balan ([email protected]) Received: 22 March 2021 – Revised: 14 June 2021 – Accepted: 22 June 2021 – Published: 19 July 2021 Abstract. The infrared absorption spectrum of a natural antigorite sample from New Caledonia is compared to its theoretical counterpart computed for the pristine antigorite m D 17 polysome within the density functional perturbation theory framework. The theoretical model reproduces most of the bands related to Si-O stretching −1 −1 in the 800–1300 cm range, OH libration, hindered OH translation and SiO4 bending in the 400–800 cm range, and OH stretching in the 3500–3700 cm−1 range. Most of the observed bands have a composite nature involving several vibrational modes contributing to their intensity, except the apical and one of the basal Si-O stretching bands whose intensity is carried by a single mode.
Studies of Celadonite and Glauconite

Studies of Celadonite and Glauconite GEOLOGICAL SURVEY PROFESSIONAL PAPER 614-F Studies of Celadonite and Glauconite By MARGARET D. FOSTER SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY GEOLOGICAL SURVEY PROFESSIONAL PAPER 614-F A study of the compositional relations between celadonites and glauconites and an interpretation of the composition of glauconites UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1969 UNITED STATES DEPARTMENT OF THE INTERIOR WALTER J. HIGKEL, Secretary GEOLOGICAL SURVEY William T. Pecora, Director For sale by the Superintendent of Documents, U.S- Government Printing Office Washington, D.C. 20402 - Price 40 cents (paper cover) CONTENTS Page Abstract.-_ ____-____-_--__-_-___--______-__-_______ Fl Interpretation of glauconite coniposition___-___________ F13 Introduction.______________________________________ 1 Relation between trivalent iron and octahedral aluminurn____________________________________ 13 Selection of analyses and calculation of atomic ratios___ 2 The Fe+3 :Fe+2 ratio_______________________ 13 Relation between the composition of celadonites and Relation between iron and potassium____________ 14 glauconites_ _ ___________________________________ 3 Fixation of potassium___________________________ 14 High potassium celadonites and glauconites-_______ 7 Deficiency in potassium content-_________________ 14 Relation between glauconite composition and geo Low potassium celadonites and glauconites_________ logic age_____________________________________ 15 Relation between Si, R+2 (VI), Al(VI), and R+3 (VI)_
Spectral Evolution Gold Exploration

spectral evolution Gold Exploration SPECTRAL EVOLUTION’s oreXpress and oreXpress Platinum with EZ-ID software for mineral identification are well-suited for gold exploration. These rugged, field spectrometers can be used in field mapping and mineral identification for many different gold deposit types, including: Paleoplacer deposits Massive sulfides Hot spring deposits Low sulfidation High sulfidation Breccia pipes Porphyry gold deposits Skarns Orogenic deposits Carbonate placements Greenstone belts oreXpress and oreXpress Platinum spectrometers are ideal With our oreXpress spectrometers and EZ-ID software, geologists can scan and identify for single-user field exploration in common alteration minerals, such as: gold mining. For low sulfidation: illite, kaolinite, chlorite, illite/smectite, buddingtonite, epidote, montmorillonite, zeolite, quartz, calcite, hematite For high sulfidation: alunite, opal, dickite, pyrophyllite, diaspora, zunyite, topaz, illite, kaolinite, chlorite, epidote, quartz, montmorillonite, goethite, jaosite, hematite For orogenic gold: muscovite, paragonite muscovite, roscoelite, illite, kaolinite, quartz, siderite, ankerite, calcite, dolomite, carbonates Using EZ-ID with the USGS spectral library, or the SpecMIN™ library available from Spectral International, the software quickly provides accurate matching of an unknown target with a known mineral spectra. With an oreXpress spectrometer and EZ-ID a geologist can identify minerals indicating gold in real-time, in the field. Benefits include: Quickly collect a lot of scans EZ-ID software identifies minerals Cover more ground in less time for better mapping in real-time by matching your Collect more accurate data for a more complete picture of the area target spectra against a known you are exploring spectral library such as the USGS Get results immediately instead of waiting for lab analysis library, or the SpecMIN library.
Current Best Practices for Vermiculite Attic Insulation

What is vermiculite insulation? What if I occasionally have to go into Vermiculite is a naturally occurring mineral that has my attic? the unusual property of expanding into worm-like EPA and ATSDR strongly recommend that accordion shaped pieces when heated. The homeowners make every effort not to disturb expanded vermiculite is a light-weight, fire- vermiculite insulation in their attics. If you resistant, absorbent, and odorless material. These occasionally have to go into your attic, current best properties allow vermiculite to be used to make practices state you should: numerous products, including attic insulation. 1. Make every effort to stay on the floored part Do I have vermiculite insulation? of your attic and to not disturb the Vermiculite can be purchased in various forms for insulation. various uses. Sizes of vermiculite products range 2. If you must perform activities that may from very fine particles to large (coarse) pieces disturb the attic insulation such as moving nearly an inch long. Vermiculite attic insulation is a boxes (or other materials), do so as gently pebble-like, pour-in product and is usually light- as possible to minimize the disturbance. brown or gold in color. The pictures in the center of What should I do if I have 3. Leave the attic immediately after the this pamphlet and on the cover show several disturbance. samples of vermiculite attic insulation. vermiculite attic insulation? 4. If you need work done in your attic such as DO NOT DISTURB IT. Any disturbance has the the installation of cable or utility lines, hire trained and certified professionals who can Is vermiculite insulation a problem? potential to release asbestos fibers into the air.
Duration of Hydrothermal Activity at Steamboat Springs, Nevada, from Ages of Spatially Associated Volcanic Rocks

Duration of Hydrothermal Activity at Steamboat Springs, Nevada, From Ages of Spatially Associated Volcanic Rocks GEOLOGIC AiL SURVEY PROFESSIONAL PAPER 458-D Duration of Hydrothermal Activity at Steamboat Springs, Nevada, From Ages of Spatially Associated Volcanic Rocks By M. L. SILBERMAN, D. E. WHITE, T. E. C. KEITH, and R. D. DOCKTER GEOLOGY AND GEOCHEMISTRY OF THE STEAMBOAT SPRINGS AREA, NEVADA GEOLOGICAL SURVEY PROFESSIONAL PAPER 458-D UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1979 UNITED STATES DEPARTMENT OF THE INTERIOR CECIL D. ANDRUS, Secretary GEOLOGICAL SURVEY H. William Menard, Director Library of Congress Cataloging in Publication Data Main entry under title: Duration of hydrothermal activity at Steamboat Springs, Nevada, from ages of spatially associated volcanic rocks. (Geology and geochemistry of the Steamboat Springs area, Nevada) (United States. Geological Survey. Professional paper ; 45 8-D) Bibliography: p. D13-D14. 1. Geothermal resources-Nevada-Steamboat Springs. 2. Geology- Nevada Steamboat Springs. 3. Potassium-argon dating. I. Silberman, Miles L. II. Series. III. Series: United States. Geological Survey. Professional paper ; 45 8-D. QE75.P9no. 458-D [GB1199.7.N3] 557.3'08s [553] 79-16870 For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 Stock Number 024-001-03215-5 CONTENTS Page Abstract __________ _______.._____________ Dl Potassium-argon ages Continued Introduction ______________________________________________ 1 Rhyolite domes______________________
Greensand.Pdf

www.natureswayresources.com GREENSAND Greensand is a naturallyoccurring mineral mined from ocean deposits from a sedimentary rock known as “Glauconite”. It is often an olive-green colored sandstonerock found in layers in many sedimentary rock formations. Origin of Greensand Greensand forms in anoxic (without oxygen) marine environments that are rich in organic detritus and low in sedimentary inputs. Some greensands contain marine fossils (i.e. New Jersey Greensand). Greensand has been found in deposits all over the world. The greenish color comes from the mineral glauconite and iron potassiumsilicate that weathers and breaks down releasing the stored minerals. The color may range from a dark greenish gray, green-black to blue-green dependingon the minerals and water content. It often weatherseasilyand forms nodules that have been oxidized with iron bearing minerals that has a reddish brown or rust color. +3 The major chemical description is ((K,Na)(Fe , Al, Mg)2(Si,Al)4O10(OH)2) General chemical information: Iron (Fe) 12-19% Potassium (K) 5-7 % Silicon (Si) 25.0% Oxygen (O) 45% Magnesium (Mg) 2-3 % Aluminum (Al) 1.9 % Sodium (Na) 0.27% Hydrogen (H) 0.47% Over 30 other trace minerals and many micronutrients. Types of Greensand Glauconite is the namegiven to a group of naturally occurring iron rich silica minerals that may be composed of pellets or grains. When glauconite is mined the upper layers that have weathered and become oxidizedand minerals are released.These sometimes form pyrite a iron sulfide (FeS2) when oxygen is www.natureswayresources.com absent. In the deeper layers or reduced zone pyrite crystals often form.