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Mineralogy and Crystal Structures of Barium Silicate Minerals

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Mineralogy and Crystal Structures of Barium Silicate Minerals MINERALOGY AND CRYSTAL STRUCTURES OF BARIUM SILICATE MINERALS FROM FRESNO COUNTY, CALIFORNIA by LAUREL CHRISTINE BASCIANO B.Sc. Honours, SSP (Geology), Queen's University, 1998 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES (Department of Earth and Ocean Sciences) We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA December 1999 © Laurel Christine Basciano, 1999 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of !PcX,rU\ a^/icJ OreO-^ Scf&PW The University of British Columbia Vancouver, Canada Date OeC S/79 DE-6 (2/88) Abstract The sanbornite deposits at Big Creek and Rush Creek, Fresno County, California are host to many rare barium silicates, including bigcreekite, UK6, walstromite and verplanckite. As part of this study I described the physical properties and solved the crystal structures of bigcreekite and UK6. In addition, I refined the crystal structures of walstromite and verplanckite. Bigcreekite, ideally BaSi205-4H20, is a newly identified mineral species that occurs along very thin transverse fractures in fairly well laminated quartz-rich sanbornite portions of the rock. It post dates the other associated barium silicates and represents either a later primary phase from intruded fluids or a product of alteration of pre-existing Ba-rich minerals, possibly sanbornite. It is colourless and forms poorly developed crystalline masses parallel to the fracture direction. There are two perfect cleavages {010} and {001}. Bigcreekite is biaxial negative, with indices of refraction a 1.537(2), p 1.538(2), y 1.541(2); X = b, Y = a, Z = c and 2Vmeas = 59.2(5)°, 2Vcalc = 60.1 °. The crystal structure of bigcreekite was solved in space group Prima to R = 3.65%, with cell parameters a 5.038(6), b 9.024(3), c 18.321 (6) A, and Z = 4. The empirical formula of 3 bigcreekite (based on 9 O) is (Ba,.0Na0.01)1.1Si,.99Hg.02O9. Dcalc = 2.739 g/cm and Draeas = 2.66(3) g/cm3. Bigcreekite is a hydrous chain silicate containing four-membered rings which form chains of silica tetrahedra, parallel to [100] and staggered in the [001] direction. Water molecules fill the large spaces between the rows of silicon tetrahedra. Bigcreekite has similarities to sanbornite and gillespite. Bigcreekite was named for Big Creek, California, its type locality. UK6, ideally (Si, Al)4Ba3C109(Cl, H20)4, is a newly identified mineral species that is light blue-grey, with one perfect cleavage on {0001}, and forms irregular masses up to 10 mm ii enclosed in parallel-bedded sanbornite-quartz rock. UK6 is uniaxial negative, with indices of refraction e 1.594(2), co 1.642(2). The crystal structure of UK6 was solved in space group P63mc to R = 4.85%, with cell parameters a 5.2432(7), c 29.859(6) and Z = 2. The empirical formula of UK6 (based on 7 cations and 2 H20 per formula unit) is (Baj97, Na003, Cao01)301(Si263 , Al, 34, 3 Ti0.03)4ClO9(Cl, 61, 2H20, F005)3 66, and Dcalc = 3.709 g/cm . The UK6 structure is based on double tetrahedral layers, [T4Og]„„, consisting of six-membered rings, with three layers of barium polyhedra connecting the tetrahedral layers. UK6 is part of the Monteregianite-(Y)- Wickenburgite series (Struntz classification) and is structurally and chemically similar to cymrite. The crystal structure of walstromite was originally solved by Glasser & Glasser (1968) in space group P1 using photographic methods to an R index of 16 %. It was redetermined in space group PJ with unit cell parameters a 6.733(1), b 9.608(2), c 6.685(1) A, a 69.64(3), p 102.29(3), y 96.89(3)°, Z = 2 to an R index of 3.8 %. The empirical formula of walstromite (based on 9 anions per formula unit) is (Ca, 947, Na^,,), 958Ba, 021(Si2995, Al0 023)3 018O9 which is similar to the formula determined by Glasser & Glasser (1968). The walstromite structure consists of trigonal rings of silica tetrahedra arranged in layers on (101) with barium and calcium atoms lying approximately halfway between the silicon tetrahedral rings, perpendicular to the a axis. Walstromite is isostructural with margarosanite, as predicted by Glasser & Glasser (1968). The crystal structure of verplanckite was originally solved by Kampf et al. (1973) in space group P6/mmm to an R index of 10.2 %. It was redetermined in P6/mmm with unit cell parameters a 16.300(2) c 7.169(1) A, Z = 3 to an R index of 4.0 %. The empirical formula of verplanckite (based on 12 Si and Al per formula unit) is (Ba]276, Ca^ Na021)1298(Mn4 54, Tiu9, Fe Mgo.o3> o.2)6.i7(Siii.66> Al0 34)I203178(C123 64, F049)2413, which is significantly different than analyses iii obtained by Alfors et al. (1965) and Kampf et al. (1973) due to the large variation in chemistry. Verplanckite is a framework structure consisting of four-membered tetrahedral rings and square pyramid polyhedra which form open hexagonal rings, with barium polyhedra located along the inner edges of the rings. There is a large degree of disorder in the verplanckite structure. Verplanckite is similar to the zeolite group of minerals with a very open framework. Table of Contents Abstract ii Table of Contents v List of Tables viii List of Figures ix Acknowledgments xii 1.0 Introduction 1 1.1 Geochemistry of Barium 1 1.2 Barium Coordination 4 1.3 Geological Occurrence of Barium Minerals 5 1.3.1 Vein and Cavity-Filling Barite Deposits 5 1.3.2 Residual Barite Deposits 5 1.3.3 Bedded Barite Deposits 6 2.0 Area Geology 8 2.1 Introduction 8 2.2 Regional Geology 11 2.3 Local Geology and Mineralogy 15 2.2.1 Sanbornite assemblage 18 2.2.2 Quartz and Walstromite Assemblage 23 3.0 Experimental Procedure 29 3.1 Crystal selection and preparation 29 3.2 Data collection 30 3.3 Structure Solution by Patterson Methods 32 3.4 Structure Refinement 34 3.5 Errors 37 3.6 Programs and Procedure 37 3.6.1 MISSYM 38 3.6.2 STR UCTURE TIDY 38 3.7 Electron-probe Microanalysis 39 3.8 Infrared Spectroscopy 40 3.9 Bond Valence 40 3.10 Gladstone Dale Rule 41 4.0 Bigcreekite: New Mineral Description 43 v 4.1 Introduction 43 4.2 Occurrence 43 4.3 Physical and Optical Properties 45 4.4 Chemical Composition 46 4.41 Electron-microprobe analysis 46 4.42 Infrared analysis 49 4.5 X-ray Crystallography and Crystal-Structure Determination 49 4.51 Experimental 49 4.52 Structure solution and refinement 51 4.6 Description of the Structure 55 4.6 Discussion 61 5.0 UK6: New Mineral Description 67 5.1 Introduction 67 5.2 Occurrence 67 5.2 Physical and Optical Properties 69 5.4 Chemical Composition 69 5.5 X-ray Crystallography and Crystal-structure Determination 72 5.5.7 Unit Cell and Space Group Determination 72 5.5.2 Experimental 78 5.53 Crystal Structure Solution and Refinement 78 5.6 Description of the Structure 80 5.7 Discussion 92 6.0 Walstromite: Refinement 98 6.1 Introduction 98 6.2 Previous Work 98 6.3 Electron-probe Microanalysis 100 6.4 X-ray Crystallography and Crystal-Structure Refinement 103 6.41 Experimental 103 6.42 Structure solution and refinement 106 6.5 Description of the Structure Based on Earlier Work 107 6.6 Description of the Structure Based on This Work 107 6.7 Discussion 117 7.0 Verplanckite: Refinement 123 7.1 Introduction 123 7.2 Previous Work 123 7.3 Electron-probe Microanalysis 124 7.4 X-ray Crystallography and Crystal-Structure Refinement 127 7.41 Experimental 127 7.42 Structure solution and refinement 130 7.5 Description of the Structure Based on Earlier Work 134 vi / 7.6 Description of the Structure Based on This Work 134 7.7 Discussion 139 8.0 Conclusion 144 8.1 Bigcreekite, UK6, Walstromite and Verplanckite 144 8.2 Future Research 146 9.0 References 148 vii List of Tables 2.1 Minerals found in sanbornite deposits at Fresno County, California. 9 2.2 Ages of deposits (Hinthorne 1974) 12 4.1 X-ray powder-diffraction data for bigcreekite (Pers. comm., A Roberts). 47 4.2 Electron-probe microanalysis of bigcreekite. 48 4.3 Miscellaneous information for bigcreekite. 50 4.4 Atomic parameters for bigcreekite. 52 4.5 ' Selected interatomic distances (A) and angles (°) for bigcreekite. 53 4.6 Bond-valence arrangement in bigcreekite. 54 5.1 Electron-probe microanalysis of UK6. 73 5.2 Miscellaneous information for UK6. 79 5.3 Atomic parameters for UK6. 81 5.4 Selected interatomic distances (A) and angles (°) for UK6. 82-83 5.5 Bond-valence arrangement in UK6. 84 6.1 Cell dimensions of walstromite. 101 6.2 Atomic coordinates for walstromite (Glasser & Glasser 1968) 102 6.3 Electron-probe microanalysis of walstromite. 104 6.4 Miscellaneous information for walstromite. 105 6.5 Final atomic parameters for walstromite. 108 6.6 Selected interatomic distances (A) and angles (°) for walstromite.
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