DOCSLIB.ORG

Neutron Diffraction Refinement of an Ordered Orthoclase Structure

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Neutron Diffraction Refinement of an Ordered Orthoclase Structure American Mineralogist, Volume 58,pages 500-507, 1973 NeutronDiffraction Refinement of an orderedorthoclase Structure Erweno PnrNcB Inst,ttute for Materials Research, National Bureau o.f Sta:ndards, Washington, D. C. 20234 Gnenrprrp DoNNnylNo R. F. MenrrN Department of Geological Sciences, McGiII Uniuersity, Montreal, Canada Abstract The crystal structure of a pegmatitic monoclinic potassium feldspar, (IG rnnonn) "Nao (Si,,*Al'*) t0"*(OH)o.1, from the Himalaya mine in the Mesa Grande pegmatitedistrict, California, has been refined with 3-dimensionalneutron-diffraction data to an unweighted R value of 0.031 for 721 symmetry-independentobserved reflections. Atomic coordinatesdiffer by no more than 3 estimated standard deviations from those of Spencer B adularia, yet the specimen does not have the adularia morphology, and no diffuse reflections with (h + k) odd have been observed.Direct refinement of the tetrahedral cation distribution shows that the Al content of the T(2) sites is not significantly different from zero (actually -0.016 with an e.s.d. of 0.029); in other words the Al-Si ordering in the tetrahedral sites is essentially complete. The mean SiO distance in the T(2) sites is 1.616A, appreciably greater than the values predicted by various regression lines relating bond distance to aluminum content. This indicates that the observed mean T,(m)-O, ?,(O)-O, and Tn(m)-O bond lengths re- ported for low albite and maximum microcline are consistentwith full Si occupancy. This ordered orthoclase occurs in gem pockets in a microcline-bearingpegmatite. The association suggestsstable growth of ordered orthoclase above the field of stability of microcline and metastablepersistence to lower temperatures.Perhaps because of more rapid crystal growth, the bulk of the pegmatitic K-feldspar ordered to common orthoclase, then transformed to maximum microcline. Introduction interestingaspect became apparent: the refinement During a continuing study of the occurrence of of the structureof this feldspar, which was classified hydroxyl ions and water molecules in minerals, a as orthoclaseon the basisof chemicalcomposition, valence sum (Donnay and Allmann, apparentsymmetry from the powder pattern,angle 197A) was per- o), formed on orthoclase,using published atomic param- betweenoptic axes (2V" = 63" i.1 and mor- eters (Jo,nesand Taylor, 1960; Colville and Ribbe, phology,indicated essentially complete order of the 1968). This summation showed a low value of the aluminum and silicon cations between the T(1) sum for the oxygen atom in position O", and, there- and T (2) tetrahedral sites, although the mean fore, a neutron difiraction study of a feldspar crystal Z-O distancesfor thesesites would haveindicated was undertaken to investigate the possible substitu- lessthan completeorder accordingto the published tion of small amounts of OH- for the oxygen in this regressionlines (Jones, 1968; Ribbe and Gibbs, position. However, even before our own negative 1969). The pulposeof this paper is to describethe results were obtained, a neutron refinement of a refinementof the structure,to comparethe results sanidine structure (Brown, Hamilton, Prewitt, and with thoseof studieson similar crystals,and to dis- Sueno, 1971) ruled out any measurableamount of cussthe implicationsour findingsmay have on feld- H in this feldspar species. Infrared absorption spar mineralogy. spectra of clear hydrothermal feldspar have shown no evidence of hydroxyl-for-oxygen substitution SpecimenDescription (J. Zemann, private communication, August 10, The neutron diftraction data were collectedfrorn 1,971,). a cleavagefragment taken from an overgrowthwhich As the investigation progressed,however, another occurs on perthite individualsfrom the Himalaya 500 NEATRON DIFFRACTION OF AN ORDERED ORTHOCLASE 501 tourmalinemine (Jahns,1954,map 8, locality20) in the Mesa Grande pegmatitedistrict, San Diego County, California. As in other granite pegmatite dikesof SanDiego County,long pendantsof micro- MICROCLINEPERTHITE cline perthite having quafiz rods in graphic inter- WITH GRAPHICQUARTZ growth grow from the hanging wall (Figure 1). Towardsthe core of the pegmatite,the quartz rods die out abruptly,presumably in responseto slower ORTHOCLASEPERTHITE crystalgrowth, and massiveqvartz aggregatesform GEMORTHOCLASE separatebodies next to microclineperthite (Jahns OVERGROWTH and Wright, 1951).Nearer the gempockets, micro- cline perthitegives way to orthoclaseperthite; these POCKETPEGMATI perthites are coated by a single-phaseorthoclase MASSIVEQUARTZ overgrowthup to I cm thick where they project into the gem pockets.Simpson (1962) suggestsa hydrothermal origin for the microcline perthite- quartzintergrowths from this area.Jahns and Burn- ham (1969, p. 856) proposegrowth of relatively Fro. 1. Cross section of an asymmetrically-zonedpegma- Burnham few feldsparnuclei from an aqueousfluid, with the tite dike. modified after Figure 58 of lahns and (1969). Thicknessof dike is measuredin meters' The clear, transportedthrough the fluid from an constituents single-phase overgrowth (labeled "gem orthoclase over- adjacentsilicate melt. The presenceof hydrothermal growth"), which coats orthoclase perthites which project fluids is further suggestedby corrosionfeatures ob- into gem pocket, yielded the specimensused in this study' served on distal portions of blocky perthites (cl The country rock is gabbroic. Simpson,1964, p.23) andby fluid inclusionsin the feldspars.The overgrowthpostdates the main epi- 19'72).A value of.0.47 percentRb'2O sode of corrosion;it occursin pocketsin associa- munication, by wet chemical analysisof the tion with gem tourmaline, beryl, qvaftz, and fine- has been found which the neutron crystal was ob- grainedmuscovite, which alsocoats the etchfeatures. specimenfrom (S. Horska, private communication,1972), Jahnsand Wright (1951) note the occurrenceof a tiined by the value of 0.49 percent clear variety of orthoclase("dental spar") among and this is confirmed analysis(Table 1)' pocketpegmatite minerals in the adjacentPala dis- Rb2O from the electron-probe trict, and mentionthat microclineis subordinatein Procedure such pockets. Experimental Table 1 is a summaryof chemicaland crystal- The cleavage fragment used in the neutron refinement lographic data on this crystal, along with similar weighs 48.356 mg so that on the basis of an observedden- It was information, as given by Colville and Ribbe, for sity of 2.563g/cm",it has a volumeof about 19 mm'' with its D axis approximately but not exactly SpencerB adulariaand SpencerC orthoclase.X-ray mounted parallel to the d axis of a computer-controlled,4-circle, neu- rasterscan images of a portion of the neutroncrys- difiractometer at the National Bureau of Standards - tron tal, at a scaleof 100 p 3.5 cm, givenoindication Reactor (Alperin and Prince, 1970). All reflections with 20 angle of Na and K inhomogeneity(S, Horska, private x2 -5" and within a spheredefined by a limiting by a communication).No variationsin A1 to Si ratio of tOO' and a wavelength of 1.232A were measured wbich first measured the intensity at the peak were noted in additionalelectron-microprobe analy- procedure position and at background positions on either side' If ses;no correlationcan be madewith the very subtle ihe peak intensity did not exceed the mean background variationsin extinction angle,well within 1o, that by at least 2a (o - (1,, ! It)'/"), the reflection was con- are found in the untwinnedovergrowth. sideredto be "unobserved",and assignedan upper limit of greater than R. H. Jahns and A. A. Chodos (unpublished intensity based on o. If the peak intensity was measuredby a 0'20step scan' If the peak data) consistentlyfind rubidium and cesium en- 2a, the peak was intensity exceeded1000 counts, the counting time was re- riched in the pocket orthoclasecrystals of the San duced in order to avoid spendingtime on meaninglesssta- Diego County pegmatites;one specimenof Hima- tistical precision. laya orthoclaseovergrowth contains 0.11 percent For each observed reflection the integrated intensity was RbzO and 0.014 CszO (R. H. Jahns,private com- determined, and from it a value of the structure factor, F' and 502 PRINCE, DONNAY, AND MARTIN Ta.eI.n1. Compositions and Crystal Data of PotassiumFeldspars Chenlcal Analysis Hlnalava Hlnalaya , Spencer B Spencer C weight percent orthoclase? orthoclase- aduLaria* orthoclase* s102 o).Jz tt tt (1 R 64.2 &zo: L8.25 18.45 18.5 18.3 Kzo L4,25 14,76 15.1 15.3 Na20 1.12 1.08 1.1 no UAU 0.'0s nll 0. 01 0.1 Sr0 nar nil 0.5 0.1 Ba0 0.25 nnt o.7 0.1 Rbr0 0,47 0.49 Hzo' o,44 H2o 0. 02 TOTAL 100.1 7 100.19 99.25 99.0 (K9. Formulabas€d on 4(st, At) (Kg.gaNa6.1gRbo.olp0.05) (K6.g6Na9.16tr6.94) (K9.9gNa6.19Ba9.61) 91Na6.66Ca6.91) per F,U. (r4artin & Donnay ' (s1:.01A19.99) (sr3.66r'11.s6) (s12 (s12 L97z):z=4 .96A11.62) .99Ar1.91) [07.96oH6.641 [07.950H6.64I [07.93(on) 6,62 I oe.oo Fomula welght: 275,80 275.27 276.72 277.05 wavelength used (l) I .54051 not glven not glven a (A) 8. s532(11) 8.554(2) L 561(2) b(i) 12.953 (14) L2,970 (4) L2.996(4) c (A) 7 ,2099(Lr) 7.2o7 (2) 7.L92(2) 90" 90" 90' B 115"073(9) 116.007 (r0) ' 115. 010(10) . Y 90" 90" 90" v(43) 718. 90(11) 7L8,7 718.9 Dga1.(8/ct3) 2,543 2.557 2.559 oo6"(g/cm3) 2. s53(1) 2.566 2,563 at 230c 2vo 63" 58,4' 43.6' Observeddiffuse reflectlons (h + k) odd t'llet chenlcal analysls by S. Horska, McGlll Unlverslty. HrO+ deslgnates H20 llberated between llToC and 1000.C. +Analytlcal data obtained by C. C. Hadldlacos on the electron nlcroprobe of the Geophysical Laboratory, Carnegle Instltutlon of Washlngton. *Data fron colvllle and Rrbbe (1968, Table 1). The glven forrrulae dlffer sllght1yi the conversion factor used by colvllle and Rlbbe ls based on 8 oxygen atons per ceil. optic axlal angles (i voi'fror Spencer (1937), /1A11 dlmensions for Hlnalaya orthoclase determlned by R. F. Martln, its standarddeviation, op, basedon counting statistics.At this (1951). The scattering factor for the tetrahedral sites was stage a systematiccomparison of pairs of reflectionsof the assumedinitially to be that for Si, which is 0.42 X 10-nm type hkl and, h*l was made in order to determine whether a (Bacon, 1972).
Load more

Recommended publications
  • Bedrock Geology Glossary from the Roadside Geology of Minnesota, Richard W
    Minnesota Bedrock Geology Glossary From the Roadside Geology of Minnesota, Richard W. Ojakangas Sedimentary Rock Types in Minnesota Rocks that formed from the consolidation of loose sediment Conglomerate: A coarse-grained sedimentary rock composed of pebbles, cobbles, or boul- ders set in a fine-grained matrix of silt and sand. Dolostone: A sedimentary rock composed of the mineral dolomite, a calcium magnesium car- bonate. Graywacke: A sedimentary rock made primarily of mud and sand, often deposited by turbidi- ty currents. Iron-formation: A thinly bedded sedimentary rock containing more than 15 percent iron. Limestone: A sedimentary rock composed of calcium carbonate. Mudstone: A sedimentary rock composed of mud. Sandstone: A sedimentary rock made primarily of sand. Shale: A deposit of clay, silt, or mud solidified into more or less a solid rock. Siltstone: A sedimentary rock made primarily of sand. Igneous and Volcanic Rock Types in Minnesota Rocks that solidified from cooling of molten magma Basalt: A black or dark grey volcanic rock that consists mainly of microscopic crystals of pla- gioclase feldspar, pyroxene, and perhaps olivine. Diorite: A plutonic igneous rock intermediate in composition between granite and gabbro. Gabbro: A dark igneous rock consisting mainly of plagioclase and pyroxene in crystals large enough to see with a simple magnifier. Gabbro has the same composition as basalt but contains much larger mineral grains because it cooled at depth over a longer period of time. Granite: An igneous rock composed mostly of orthoclase feldspar and quartz in grains large enough to see without using a magnifier. Most granites also contain mica and amphibole Rhyolite: A felsic (light-colored) volcanic rock, the extrusive equivalent of granite.
    [Show full text]
  • An Investigation Into the UV Fluorescence of Feldspar Group
    An Investigation into UV Fluorescence in Feldspar Group Minerals Natasha Morrison Submitted in Partial Fulfillment of the Requirement for the Degree of Honours Bachelor of Science, Department of Earth Sciences At Dalhousie University Halifax, Nova Scotia March 17th, 2013 Submitted to: Dr. Richard Cox Dr. Martin Gibling 1 Distribution License DalSpace requires agreement to this non-exclusive distribution license before your item can appear on DalSpace. NON-EXCLUSIVE DISTRIBUTION LICENSE You (the author(s) or copyright owner) grant to Dalhousie University the non-exclusive right to reproduce and distribute your submission worldwide in any medium. You agree that Dalhousie University may, without changing the content, reformat the submission for the purpose of preservation. You also agree that Dalhousie University may keep more than one copy of this submission for purposes of security, back-up and preservation. You agree that the submission is your original work, and that you have the right to grant the rights contained in this license. You also agree that your submission does not, to the best of your knowledge, infringe upon anyone's copyright. If the submission contains material for which you do not hold copyright, you agree that you have obtained the unrestricted permission of the copyright owner to grant Dalhousie University the rights required by this license, and that such third-party owned material is clearly identified and acknowledged within the text or content of the submission. If the submission is based upon work that has been sponsored or supported by an agency or organization other than Dalhousie University, you assert that you have fulfilled any right of review or other obligations required by such contract or agreement.
    [Show full text]
  • The System Quartz-Albite-Orthoclase-Anorthite-H2O As a Geobarometer: Experimental Calibration and Application to Rhyolites of the Snake River Plain, Yellowstone, USA
    The system quartz-albite-orthoclase-anorthite-H2O as a geobarometer: experimental calibration and application to rhyolites of the Snake River Plain, Yellowstone, USA Der Naturwissenschaftlichen Fakultät der Gottfried Wilhelm Leibniz Universität Hannover zur Erlangung des Grades Doktor der Naturwissenschaften (Dr. rer. nat.) vorgelegte Dissertation von M. Sc. Sören Wilke geboren am 22.08.1987 in Hannover ACKNOWLEDGEMENTS I would first like to acknowledge the Deutsche Forschungsgemeinschaft (DFG) for funding the project HO1337/31 Further thanks to my supervisors for their support: Prof. Dr. François Holtz and Dr. Renat Almeev. I would also like to thank the reviewers of this dissertation: Prof. Dr. François Holtz, Prof. Dr. Eric H. Christiansen and Prof. Dr. Michel Pichavant. This research would not have been possible without massive support from the technical staff of the workshop and I owe thanks especially to Julian Feige, Ulrich Kroll, Björn Ecks and Manuel Christ. Many thanks to the staff of the electron microprobe Prof. Dr. Jürgen Koepke, Dr. Renat Almeev, Dr. Tim Müller, Dr. Eric Wolff and Dr. Chao Zhang and to Prof. Dr. Harald Behrens for help with IHPV and KFT. Thanks to Dr. Roman Botcharnikov and Dr. David Naeve for their ideas on experimental and statistical procedures. Operating an IHPV is challenging and I would like to thank Dr. Adrian Fiege and Dr. André Stechern for teaching me how to do it and helping me with troubleshooting. I would like to thank Carolin Klahn who started the work that I herewith complete (hopefully) and Torsten Bolte who provided samples and know how on the Snake River Plain.
    [Show full text]
  • Rock and Mineral Identification for Engineers
    Rock and Mineral Identification for Engineers November 1991 r~ u.s. Department of Transportation Federal Highway Administration acid bottle 8 granite ~~_k_nife _) v / muscovite 8 magnify~in_g . lens~ 0 09<2) Some common rocks, minerals, and identification aids (see text). Rock And Mineral Identification for Engineers TABLE OF CONTENTS Introduction ................................................................................ 1 Minerals ...................................................................................... 2 Rocks ........................................................................................... 6 Mineral Identification Procedure ............................................ 8 Rock Identification Procedure ............................................... 22 Engineering Properties of Rock Types ................................. 42 Summary ................................................................................... 49 Appendix: References ............................................................. 50 FIGURES 1. Moh's Hardness Scale ......................................................... 10 2. The Mineral Chert ............................................................... 16 3. The Mineral Quartz ............................................................. 16 4. The Mineral Plagioclase ...................................................... 17 5. The Minerals Orthoclase ..................................................... 17 6. The Mineral Hornblende ...................................................
    [Show full text]
  • Geochemistry and Genesis of Beryl Crystals in the LCT Pegmatite Type, Ebrahim-Attar Mountain, Western Iran
    minerals Article Geochemistry and Genesis of Beryl Crystals in the LCT Pegmatite Type, Ebrahim-Attar Mountain, Western Iran Narges Daneshvar 1 , Hossein Azizi 1,* , Yoshihiro Asahara 2 , Motohiro Tsuboi 3 , Masayo Minami 4 and Yousif O. Mohammad 5 1 Department of Mining Engineering, Faculty of Engineering, University of Kurdistan, Sanandaj 66177-15175, Iran; [email protected] 2 Department of Earth and Environmental Sciences, Graduate School of Environmental Studies, Nagoya University, Nagoya 464-8601, Japan; [email protected] 3 Department of Applied Chemistry for Environment, School of Biological and Environmental Sciences, Kwansei Gakuin University, Sanda 669-1337, Japan; [email protected] 4 Division for Chronological Research, Institute for Space-Earth Environmental Research, Nagoya University, Nagoya 464-8601, Japan; [email protected] 5 Department of Geology, College of Science, Sulaimani University, Sulaimani 46001, Iraq; [email protected] * Correspondence: [email protected]; Tel.: +98-918-872-3794 Abstract: Ebrahim-Attar granitic pegmatite, which is distributed in southwest Ghorveh, western Iran, is strongly peraluminous and contains minor beryl crystals. Pale-green to white beryl grains are crystallized in the rim and central parts of the granite body. The beryl grains are characterized by low contents of alkali oxides (Na2O = 0.24–0.41 wt.%, K2O = 0.05–0.17 wt.%, Li2O = 0.03–0.04 wt.%, Citation: Daneshvar, N.; Azizi, H.; and Cs2O = 0.01–0.03 wt.%) and high contents of Be2O oxide (10.0 to 11.9 wt.%). The low contents Asahara, Y.; Tsuboi, M.; Minami, M.; of alkali elements (oxides), low Na/Li (apfu) ratios (2.94 to 5.75), and variations in iron oxide Mohammad, Y.O.
    [Show full text]
  • 44. K-Metasomatism and the Origin of Ba- and Inclusion- Zoned Orthoclase Megacrysts in the Papoose Flat Pluton, Inyo Mountains, California, USA
    1 ISSN 1526-5757 44. K-metasomatism and the origin of Ba- and inclusion- zoned orthoclase megacrysts in the Papoose Flat pluton, Inyo Mountains, California, USA Lorence G. Collins and Barbara J. Collins July 31, 2002 email:[email protected] Abstract In the Papoose Flat pluton in the Inyo Mountains of California the orthoclase megacrysts are suggested to form by K-metasomatism because microfracturing of a few normally zoned plagioclase crystals channeled introduced K-bearing fluids to these places, thereby promoting K-metasomatism and localized growth to form the megacrysts. Isochemical recrystallization to produce the megacrysts from preexisting stressed orthoclase and plagioclase crystals is ruled out because the original relatively undeformed granodiorite of the Papoose Flat pluton contained only 8-13 vol. % orthoclase that could not have been reorganized into more than 19 vol. % orthoclase in the groundmass and megacrysts and because original biotite was insufficient to supply enough K. An outside K source is required. Si- metasomatism of biotite to form quartz would have supplied some of the K. Concentrically oriented plagioclase inclusions that occur parallel to Ba-K growth zones in the megacrysts are shown to be formed from primary groundmass minerals, some of which were broken into fragments but others were not microfractured. The occurrences of myrmekite inside the megacrysts, scalloped edges on all surfaces of many plagioclase inclusions, sodic rims on irregular plagioclase inclusions against outer surfaces of former faces of the orthoclase, and disoriented inclusions that are not parallel to growth zones provide evidence for the primary origin of the inclusions. Rare trails of inclusions through the megacrysts indicate that the megacrysts are porphyroblasts and not residual phenocrysts (porphyroclasts).
    [Show full text]
  • And Fe,Mg-Chlorite: a Genetic Linkage to W, (Cu, Mo) Mineralization in the Magmatic-Hydrothermal System at Borralha, Northern Portugal
    Mineralogical Magazine, May 2018, Vol. 82(S1), pp. S259–S279 Fe-, Fe,Mn- and Fe,Mg-chlorite: a genetic linkage to W, (Cu, Mo) mineralization in the magmatic-hydrothermal system at Borralha, northern Portugal 1,* 1 2 I. BOBOS ,F.NORONHA AND A. MATEUS 1 Instituto de Ciências da Terra – Polo Porto, Departamento de Geociências, Ambiente e Ordenamento do Território, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre 687, 4169-007 Porto, Portugal 2 Departamento de Geologia e IDL, Faculdade de Ciências, Universidade de Lisboa, C6, Campo Grande, 1746-016 Lisboa, Portugal [Received 23 January 2017; Accepted 22 December 2017; Associate Editor: Krister Sundblad] ABSTRACT A genetic linkage between W, (Cu, Mo)-mineralization and chlorite minerals, and the discrimination of different mineralization events in the magmatic-hydrothermal system of Borralha, northern Portugal, is discussed on the basis of textural relationships, crystal chemistry and stable isotopic data obtained from chlorite. Chlorite minerals were identified in assemblages with quartz, feldspars, tungstates and sulfides. X-ray diffraction studies of selected chlorite minerals shows a trioctahedral structural type. Electron probe micro-analyses identified four different compositions and associations: (1) Fe,Mn-chlorite with scheelite I; (2) Fe-chlorite with wolframite + scheelite II ± sulfide; (3) Fe,Mg-chlorite with molybdenite + bismuthinite; 3+ 2+ and (4) Mg,Fe-chlorite with chalcopyrite. The composition of Fe-chlorite (Al3.01Fe0.25Fe7.95Mn0.26 3+ 2+ Mg0.19)11.66(Si5.44Al2.56)8O20(OH)8 corresponds to daphnite and Fe,Mn-chlorite (Al2.69Fe0.02 Fe7.54 Mn1.08Mg0.62)11.89(Si5.31Al2.68)4O20(OH)8 to a mixed composition between daphnite and amesite.
    [Show full text]
  • Identification Tables for Common Minerals in Thin Section
    Identification Tables for Common Minerals in Thin Section These tables provide a concise summary of the properties of a range of common minerals. Within the tables, minerals are arranged by colour so as to help with identification. If a mineral commonly has a range of colours, it will appear once for each colour. To identify an unknown mineral, start by answering the following questions: (1) What colour is the mineral? (2) What is the relief of the mineral? (3) Do you think you are looking at an igneous, metamorphic or sedimentary rock? Go to the chart, and scan the properties. Within each colour group, minerals are arranged in order of increasing refractive index (which more or less corresponds to relief). This should at once limit you to only a few minerals. By looking at the chart, see which properties might help you distinguish between the possibilities. Then, look at the mineral again, and check these further details. Notes: (i) Name: names listed here may be strict mineral names (e.g., andalusite), or group names (e.g., chlorite), or distinctive variety names (e.g., titanian augite). These tables contain a personal selection of some of the more common minerals. Remember that there are nearly 4000 minerals, although 95% of these are rare or very rare. The minerals in here probably make up 95% of medium and coarse-grained rocks in the crust. (ii) IMS: this gives a simple assessment of whether the mineral is common in igneous (I), metamorphic (M) or sedimentary (S) rocks. These are not infallible guides - in particular many igneous and metamorphic minerals can occur occasionally in sediments.
    [Show full text]
  • A Partial Glossary of Spanish Geological Terms Exclusive of Most Cognates
    U.S. DEPARTMENT OF THE INTERIOR U.S. GEOLOGICAL SURVEY A Partial Glossary of Spanish Geological Terms Exclusive of Most Cognates by Keith R. Long Open-File Report 91-0579 This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards or with the North American Stratigraphic Code. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. 1991 Preface In recent years, almost all countries in Latin America have adopted democratic political systems and liberal economic policies. The resulting favorable investment climate has spurred a new wave of North American investment in Latin American mineral resources and has improved cooperation between geoscience organizations on both continents. The U.S. Geological Survey (USGS) has responded to the new situation through cooperative mineral resource investigations with a number of countries in Latin America. These activities are now being coordinated by the USGS's Center for Inter-American Mineral Resource Investigations (CIMRI), recently established in Tucson, Arizona. In the course of CIMRI's work, we have found a need for a compilation of Spanish geological and mining terminology that goes beyond the few Spanish-English geological dictionaries available. Even geologists who are fluent in Spanish often encounter local terminology oijerga that is unfamiliar. These terms, which have grown out of five centuries of mining tradition in Latin America, and frequently draw on native languages, usually cannot be found in standard dictionaries. There are, of course, many geological terms which can be recognized even by geologists who speak little or no Spanish.
    [Show full text]
  • Minerals Explained I—Rock Forming Silicate Minerals I Craig Barrie Minerals Explained Editor
    Minerals explained I—Rock forming silicate minerals I Craig Barrie Minerals Explained editor Overview The rocks which make up the planet we live on, the houses many of us live in and helped carve the scenery we enjoy all have one thing in common, they are all made up of minerals. Every rock type—whether it be igneous, metamorphic or sedimentary is made up of a collection of one or more of these minerals, with some being common and widespread (Fig. 1A: quartz; SiO2), while others are rare, with most people never coming across them during their lives, (except perhaps in a museum, like Kinoite; Ca2Cu2Si3O8(OH)4—see Fig. 1B). Defining what actually constitutes a mineral is not as easy as it might seem and whatever scheme is used will exclude substances which some might classify as a mineral. However, the following definition would probably be agreeable to most: ‘A mineral is a naturally occurring, usually inorganic solid with a highly ordered atomic arrangement and a definite (although not fixed) chemical composition.’ This means that in order to qualify as a mineral a substance must be found to be naturally occurring in nature and not simply generated in a laboratory. For example Baddeleyite (Fig. 2A) is a naturally occurring, although rare, mineral of zirconium oxide (ZrO2) while cubic zirconia (Fig. 2B) is a laboratory synthesized variety of ZrO2, often used in the jewellery industry as a substitute for diamond, but which is not classed as a mineral. Traditional definitions of a mineral also require them to form via inorganic processes, such as from the melts inherent to igneous rocks and via the increased pressures and temperatures that define the metamorphic regime.
    [Show full text]
  • Characterization of Natural Feldspars by Raman Spectroscopy for Future Planetary Exploration
    1795 The Canadian Mineralogist Vol. 46, pp. 000 (2008) DOI : 10.3749/canmin.46.6.00 CHARACTERIZATION OF NATURAL FELDSPARS BY RAMAN SPECTROSCOPY FOR FUTURE PLANETARY EXPLORATION JOHN J. FREEMAN§, ALI A N WANG, Kar L A E. KUEBLER, Bra DL E Y L. JOLLIFF A ND Larr Y A. HASKIN† Department of Earth and Planetary Sciences and McDonnell Center for Space Sciences, Washington University in St. Louis, St. Louis, Missouri 63130, U.S.A. Abs T ra CT The Raman spectra of a large number of natural feldspar-group minerals were obtained to determine what compositional and structural information can be inferred solely from their Raman spectra. The feldspar minerals selected cover a wide range of Na, K, and Ca proportions, crystal structures and degrees of cation disorder. The samples include both homogeneous feldspar phases and a few with visible intergrowths. From the positions of the strongest Raman peak in the spectrum, four structural types of feldspars can be readily identified: orthoclase (and microcline), albite, high-temperature plagioclase, and anorthite. Using a Raman spectral database of feldspar minerals established during this study and an autonomous spectral search-and-match routine, up to seven different types of feldspar can be unambiguously determined. Three additional feldspar types can be further resolved by careful visual inspection of the Raman spectra. We conclude that ten types of feldspars can be classified according to their structure, crystallinity, and chemical composition solely on the basis of their Raman spectra. Unlike olivine, pyroxene and some Fe-oxides, the Raman peak positions of the feldspars cannot be used to extract quantitative information regarding the cation composition of the feldspar phases.
    [Show full text]
  • Intrusive Igneous Rocks, Part 2
    GLY 4310C LAB 7 INTRUSIVE IGNEOUS ROCKS, PART 2 Granite, Alkali Feldspar Granite, Granodiorite, Quartz Monzonite, and Monzonite These intrusive (plutonic) rocks correspond to fields on diagram 2-2 of Winter. These rocks are generally richer in silica and alkali feldspar than those studied in Lab 6. More information about these rocks is included in Chapter 13 and 14 of Moorhouse. GRANITE - Intrusive igneous, plutonic. Medium to coarse-grained plutonic rock containing between 20% to 60% quartz, feldspar (the plagioclase to plagioclase plus alkali feldspar (P/A+P) ratio is between 10 to 65%), and small amounts of biotite, hornblende or other silicates. K-spar may be orthoclase and/or microcline. The plagioclase is sodic, either oligoclase or andesine. Rocks of this composition are scarce and the definition is often broadened, for example by including quartz monzonite. The alkali feldspar is commonly microcline perthite (mixture of microcline and plagioclase). In some perthites, the albite and K-feldspar are completely separated, possibly due to recrystallization. The quartz is almost always anhedral in granites. The quartz grains often contain inclusions. Biotite is usually brown or brownish green and often contains inclusions. Hornblende is dark green and pleochroitic. Biotite may form a rim around the hornblende. If pyroxene (diopside) is present, hornblende may form a rim around the pyroxene. Muscovite may occur in patches around the biotite. Many granites are foliated. The name is from the Latin granum, meaning grain. ALKALI FELDSPAR GRANITE - Intrusive igneous, plutonic. Medium to coarse-grained plutonic rock containing between 20% to 60% quartz, feldspar (the plagioclase to plagioclase plus alkali feldspar (P/A+P) ratio < 10), and small amounts of biotite, hornblende or other silicates.
    [Show full text]