T 1981 the CRYSTAL STRUCTURE of RASPITE, Pbw04 By
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T 1981 THE CRYSTAL STRUCTURE OF RASPITE, PbW04 by Diane Eileen Westfahl 1977 ProQuest Number: 10782136 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a com plete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest ProQuest 10782136 Published by ProQuest LLC(2018). Copyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States C ode Microform Edition © ProQuest LLC. ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106- 1346 T 1981 A thesis submitted to the Faculty and the Board of Trustees of the Colorado School of Mines in partial ful fillment of the requirements for the degree of Master of Science. Signed: I 1 J U 1 M/t/oqaiL, £ic. Diane Eilee n w e stfahp. Goldan, Colorado Date: , 1977 Approv 'or V F i r i k e y ~ 7 ea partment of Geology Golden, Colorado Date: h </, 1977 ii T 1981 ABSTRACT Raspite, PbWO^, monoclinic, P2^ /c, a = 5.568, b = 4.978, c = 13.571 A, 8 = 107.68°, Z = 4, is one of the three known polymorphs of lead tungstate. The structure was solved by Patterson and difference syntheses. Least squares refinement converged to R = 0.092 for 630 unique reflections. Lead and tungsten positions were distinguish able on the basis of bond lengths only. The structure consists cf pairs of WO^ tetrahedra separated from each other along {100} by lead atoms result ing in the perfect {100} cleavage. Average interatomic o o distances are: W - 0, 1.9 A and Pb - 0, 2.64 A. The structure shows strong similarities to the structures of both stolzite, the natural polymorph, and PbWO^-III, the high temperature and pressure polymorph of lead tungstate. T 1981 TABLE OF CONTENTS Page Introduction ............................................. 1 Occurrence and Physical Properties of Raspite ............................................. 1 Acknowledgments................................. 6 Experimental ............................................ 7 Crystal Selection ................................. 7 Precession Photography............................. 10 Data Collection.................................... 19 Data Reduction...................................... 20 Structure Determination. ........................ 22 Fourier Synthesis ................................. 22 Patterson Map Interpretation...................... 24 The Patterson Map of Raspite. ............... 27 Structure Refinement .................................... 32 Structure Factor Calculation and Least Squares Refinement................................. 3 2 AF Synthesis........................................ 34 Discussion of the Structure............................. 40 Description........................................ 40 Sources of Error.................... 46 Comparison with Stolzite and PbW04-III........... 48 Conclusions............................................... 57 Appendix . .......................................... 60 References............................................... 73 iv T 1981 LIST OF ILLUSTRATIONS Figure Page 1. Raspite crystals .................................. 3 2. Crystal drawing.................................... 4 3. Raspite with stolzite............................. 4 4. Raspite crystal mounted for data collection. 12 5. Precession photograph of twinned crystal.... 13 6 . Precession photograph of extensively twinned crystal............................................. 14 7. Representative precession photographs..............15-18 8. Space group data - P 2 ^ / c ......................... 2 5 9. Patterson map sections........................... 30 10. Raspite structure - {010} projection ............ 43 11. WO4 tetrahedra pair................................ 44 12. Raspite structure - {100} projection ............ 45 13. Stolzite structure - {100} projection............ 50 14. Raspite structure showing distorted stolzite cell..................................... 51 15. PbWO^-III structure - {010} projection ......... 53 v T 1981 LIST OF TABLES Table Page 1. Calculation of ......................... 8 2. Calculation of Patterson peak heights............ 28 3. Raspite atomic positions and thermal parameters........................................ 41 4. Raspite bond lengths and angles................... 42 5. PbW04-III bond lengths and angles................ 54 6 . Comparison of density, coordination and bond lengths for the three lead tungstates........... 56 vi T 1981 INTRODUCTION Occurrence and Physical Properties of Raspite Raspite, PbWO^, was first discovered in 1897 by C. Hlawatsch at the Proprietary Mine, Broken Hill, New South Wales, Australia. It was named after Mr. Rasp, the dis coverer of this rich Ag, Pb, Zn deposit. There, raspite is found in cavities in Mmanganiferous oxidized vein material'’ (Dana, 1951) along with stolzite, a natural polymorph of PbWO^ which is isostructural with scheelite (figure 3). The Broken Hill district is one of the principal lead silver-zinc producing areas in the world. Discovered in 1833, the deposit is contained in a thick series of meta morphosed Precambrian sediments. The principle ore zone consists of "two or more mineralized beds of contorted gneiss... distinguished by details of gangue mineralogy and metal ratios" (Park, MacDiarmid, 1970). The primary ore minerals are galena and sphalerite but the deposit is rich in other sulfides, sulfates, tungstates, antimonides, many of them rare and unusual. At the Broken Hill deposit, a gossan of quartz, limonite, manganese oxides and hematite originally extended to a depth of 300 feet. It is probabl that raspite occurred in the gossan of the Broken Hill deposit. Raspite has also been reported in gold placers T 1981 of Soumidouro, Minas Geraes, Brazil, along with stolzite and scheelite; and in tin veins on the Cerro Estano, east of Guanajuato, Mexico. In color, raspite is light yellow, yellowish brown, or reportedly, gray. Its hardness is 2.5 to 3, with a density of 8.46 and an adamantine luster. Raspite exhibits a per fect {100} cleavage. Crystals are often tabular on {100} with this form elongated and striated parallel to [010] (figures 1 and 3). Less often, crystals are elongated along [100] or are thin and tabular on {T01}. Raspite commonly twins on {100} (figures 1 and 3} and less commonly on {T02}. The external morphology places raspite in class 2/m (Dana, 1951). A chemical analysis follows: 1 2 PbO 49.03 49.06 WO3 50.97 48.32 Rem. - 1.43 100.00 98.81 1. PbW04. 2. Broken Hill, NSW. Rem.is Fe203, MnO (in Dana, 1951). The trace of manganese and iron oxides present in raspite may indicate a very slight amount of substitution for W. Optically, raspite is biaxial (+) with a 2V nearly equal to zero. The refractive indices are: T 1981 3 Figure 1. Raspite crystals from Broken Hill, New South Wales, Australia. Length of large crystal is approxi mately 3 mm. Note twinned crystals in background. The raspite occurs on a matrix of manganese oxide bearing quartz with limonite. T 1981 4 m Figure 2. Drawing of raspite crystal from Minas Geraes, Brazil (Dana, 1951). c - {001}, b - {010}, a - {100}, m - {110}, d - {Oil}, e - {101}, p - {122}. Figure 3. Twinned raspite (r) with stolzite (s) on manganese oxide bearing quartz with limonite from Broken Hill, New South Wales, Australia. Longest crystals are approximately 3 mm in length. T 1981 5 N X 2.27 + .02 Y = b 2.27 + .02 Z 2.30 t .02 Zac = 30° (Dana, 1951) The unit cell constants are: o a = 5.58 A o b = 5.00 A o c = 13.64 A 8 - 107°33f and the space group is P2^/c. The unit cell contains Pb^(WO^)^ (Shaw and Claringbull, 1955). Several studies of the chemistry of lead tungstate have been made: Jaeger and Gerns (1921), Jung (1931), both reported in Dana (1951); and Richter, Kruger and Pistorius (1976) , but raspite has never been synthesized. Shaw and Claringbull reported that raspite transforms irreversibly to stolzite at about 400°C. The present study was undertaken in part because the raspite structure had not yet been solved and in part out of interest in possible structural similarities between raspite and stolzite as suggested by the raspite to stolzite transformation and the common occurrence of the two polymorphs together. T 1981 6 Acknowledgments During the course of this study and in thesis work prior to this study, many people have provided invaluable assistance. Dr. Cortlandt Pierpont of the University of Colorado, Department of Chemistry authorized use of the facilities there for data collection and Curt Haltiwanger collected the data and offered many helpful suggestions during completion of the structure. Thanks are due to Dr. Joseph Finney, committee chairperson and advisor, for suggesting such fascinating minerals for study, for provid ing mineral specimens for use in this study, and for his encouragement throughout. The kind assistance of Dr. Subrata Ghose during data collection and initial work on a previous thesis project, and the discussions on direct methods with Dr. Alan Tench are also gratefully acknowledged. Color photographs of raspite crystals were provided by Webster Shipley. T 1981 7 EXPERIMENTAL Crystal Selection Raspite used in this study is from British Museum specimen B. M. 1972, 300, Raspite, Stolzite, NSW. In selecting a crystal for use in a structure determination, size and shape are important. The intensities of diffracted rays from a given