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THE MICROHARDNESS of OPAQUE MINERALS VOL.I THESIS Submitted by B.B. YOUNG, B.Sc., A.R.S.M. Degree of Doctor of Philosophy In

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THE MICROHARDNESS of OPAQUE MINERALS VOL.I THESIS Submitted by B.B. YOUNG, B.Sc., A.R.S.M. Degree of Doctor of Philosophy In THE MICROHARDNESS OF OPAQUE MINERALS VOL.I THESIS Submitted by B.B. YOUNG, B.Sc., A.R.S.M. Degree of Doctor of Philosophy in the Faculty of Science UNIVERSITY OF LONDON April, 1961 Department of Mining Geology, Imperial College, London. I CONTENTS VOL. 1 Page No. Abstracts 1 Acknowledgements 4 Introduction 5 Chapter I. THEORY OF HARDNESS 9 A. General 9 B. Nature of the bonding forces 10 C. Hardness in relation to polishing 14 D. Assessement of hardness 16 E. Microhardness testing instruments 22 Chapter II. EXPERIMENTAL PROCEDURE 25 A. Methods of mounting sections 25 B. Relative merits of the mounting media used 30 C. Grinding and polishing techniques 32 D. Orientation of sections 36 E. Measurement of microhardness 44 F. Routine procedure 42 G. Accuracy and renroducibility of results 45 11 Page No. Chapter III. VARIATION OF MICROHARDNESS WITH LOAD 53 A. Variation of microhardness values with load 53 (a)General 53 (b)Results 60 (c)Discussion of the results 69 (d)Conclusions 77 B. The relation between load and grain size 78 (a)General 78 (b)Discussion 80 C. Variation of the deformation characteristics with load 88 Chapter IV. VARIATION OF MICROHATNESS WITH ORIENTATION 90 A. General 90 B. Microhardness values determined from randomly oriented sections 91 C. The relation, during indentation, between deformation processes and orientation 104 D. Microhardness values obtained on oriented sections of mineral 110 (a)General 110 (b)Discussion of the results 111 (i) Isometric minerals 111 (ii) Tetragonal minerals 130 (iii)Hexagonal mineral 139 iii Page No. (iv) Orthorhombic minerals 150 (v) Monoclinic minerals 163 (vi) Triclinic mineral E. Variation of microhardness on particular cryatal faces 169 (a) General 169 (h) Theory 169 (c) Results and discussion 174 (1) Isometric minerals 174 (ii) Tetragonal minerals 181 (iii)Hexagonal minerals 183 (iv) Orthorhombic minerals 192 (v) Monoclinic minerals 207 (vi) Triclinic minerals 209 F. The variations of Knoo,D microhardness with reflectivity on particular crystal faces. 211 G. Variation of the diagonal lengths of Vickers indentation on rotation of the indenter on particular crystal faces 213 (a)Minerals whose crystals have been accurately oriented 211+ (b)Minerals whose orientations were not precisely known 218 (c)General discussion 218 iv Page No, Chapter V. THE SHAPE AND ASSOCIATED CHARACTERISTICS OF TH2, INDENCATIONS 223 A. General 223 B. Variation in the shape of indentations 224 C. Variations in the dimensions of inden- tations 228 D. Associated deformation characteristics 229 E. Features of plastic deformation 230 F. Fracturing Phenomena 231 G. V7riations of the shape and deformation characteristics with orientation 235 H. Variations of the shape and deformation characteristics of indentations with mineral species 241 I. The relationship of indentation character- istics to atomic structure 254 Chapter VI. VARIATION OF MICROHATDNESS WITH CHANGES OF CHEICAL COMPOSITION 267 A. Introduction 267 B. Microhardness variations in chemically analysed isomorphous. series 269 C. Microhardness differences between end members of isomorphous or isostructural series 281+ D. Variations of microhardness with chemical composition between different mineral species 296 Page No. Chapter VII. SYSTEMATIC MICROHARDNESS DATA 311 A. Accuracy and reproducibility of the results 311 B. Comparison of the microhardneqs v2lues with established Mohs and Talmage hardness values 316 C. Comparison of Vickers microhardness and reflectivity results 331 D. Comparison of other physical properties of minerals with microhardness values 341 E. The relationship between microhardness, paragenetic sequence, and temperature of formation 345 F. Crystallochemical factors controlling micro- hardness 351 Chapter VIII. MINERALOGICAL APPLICATIONS OF MICROHARDNESS TESTING TECHNIQUES 359 Chapter IX. GENERAL CONCLUSIONS 364 References 378 Anpendix A. Photographs of Indentation 387 Characteristics Appendix. B. 413 vi VOL. II Page No. Introduction 417 Mineral Authentication 419 Abbreviations 420 References 422 RESULTS 423 vii List of Tables Page No I-IV A-X Distance and hardness 12 V Effect of mounting method on microhardness values 31 VI Microhardness values on and off stage 39 VII Effect of number of measurements on the probable error of the microhardness 52 VIII Relationship of orientation to the microhard= ness and logarithmic index - Galena (Vickers indenter) 55 IX Relationship of oreitnation to the micro- hardness and logarithmic index - Galena ' (Knoop indenter) 56 X Relationship of orientation to the microhard- ness and logarithmic index - Sphalerite (Vickers and Knoop)indenters) 57 XI Relationship of orientation to the micro- hardness and logarithmic index - other minerals 58, 59 XII Probable errors of the mean microhardness values and logarithmic indices 62 XIII Variation of microhardness with load on oriented sections of 10 minerals 70 . XIV-XV Effect of error in measurement of the diagonal length on the microhardness 72 XVI Optimum load dependent upon the hardness of the minerals 79 XVII Minimum Grain sizes 81 - 86 XVIII Systematic Microhardness Data 92 - 99 viii Page No. XIX Variation of the microhardness anisotropism 102 of minerals with crystal system XX Comparison of indentation and scratch micro- hardness values on the (100, (110) and (111) faces of galena 113 XXI Oriented microhardness w,lues obtained on some members of the spinel minerals 124 XXII Oriented microhardness values obtained on Gold, Conoer and Cuprite 125 XXIII Oriented microhardness values 126 - 129 XXIV The variation of microhardness and reflec- tivity values with orientation 133 - 138 XXV Comparison of the microhardness values 144 obtained by Bowie and Taylor (1958) and the present writer, on oriented sections of pyrrhotite XXVI A comparison of reflectivity and micro- hardness differences on the basal (0001) and orism (1010) faces of six hexagonal minerals 147 XXVII % Knoop microhardness anisotropism on six hexagonal minerals 188 XXVIII Comparison of Knoop microhardness maxima and minima with reflectivity maxima and minima - Hexagonal 204 XXIX Comparison of Knoop microhardness and reflectivity maxima and minima - Tetragonal and Monoclinic 205 XXX Comparison of Knoop microhardness and reflectivity maxima and minima - Orthorhombic 206 XXXI The relationship of the elongation of indentations to movement planes 221 - 222 ix Page No, XXXII Examples of minerals showing different indentation types 225 XXXIII Examples of minerals whose indentations show different degrees of "anisotropism" 226 XXXIV Translation data deduced from the present studeies 262 - 264 XXXV Deformation characteristics of the main mineral groups 265 - 266 XXXVI Microhardness mean values for 10 analysed sphalcrites 270 XXXVII Microhardness values obtained on 10 analysed huebnerite-ferbr:rites 275 XXXVIII Micrqhardness values obtained on 7 analysed columbite-tantalites 277 XXXIX Microhardness values - Native elements 298 XL Microhardness values - Sulphides, selenides and tellurides 299 - 300 XLI Microhardness values - Arsenides, antimonides, suloharsenides and sulphantimonides 301 XLII Microhardness values - Sulphosalts 302 XLIII Microhardness values - Oxides, Hydroxides 303 - 304 XLIV Microhardness values - Carbonates, phosphates 305 XLV Ionic and atomic radii - After Evans (1939) 306 YLVI Tetrahedral atomic radii - After Pauling and Huggins (1934) 307 XLVII Variation in microhardness with chemical composition in some cobalt-hearing analogues of pentlandite 308 XLVIII Comparison of calculated and actual hardness values for niccolite and breithauptite (After Povarennykh, 1959) 308 x Page No. XLIX The variation of microhardness with chemical composition in some copper iron sulphides 309 L The variation of microhardness with chemical composition in some lead sulpho- salt minerals. 309 LI The relationship between crystal system and microhardness in minerals having the compositions - ZnS and FeS2 310 LII Vickers and Knoop microhardness values for the standard Mohs scale minerals 318 LIII A comparison of Vickers mean microhardness data 319 LIV Microhardness values obtained on the standard Mohs scale minerals - After Povarennykh (1959) 322 LV Microhardness values extrapolated from Mohs and/or Talmage values 325 - 328 LVI Microhardness values extrapolated from polishing hardness data 329 - 330 LVII The relationship between bonding and the physic .l properties of minerals 344 LVIII The relationship between structure, bonding, valency, microhardness and paragenetic sequence of sulphides 347 LIX Relationship between temperatures of formation of minerals and their hardness values 349 - 350 LX A comparison of calculated and measured microhardness values 356. -1- ABSTRACT Knoop and Vickers microhardness values have been determined at different loads for over 200 mineral species. The microhardness data have been applied to a system of mineral identification, and some of the more theoretical problems associated with mineral hardness have been investi- gated. Although the minerals studied exhibited considerable variation in microhardness, the determination of the micro- hardness and reflectivity ranges and their mean values was found to be diagnostic for most of the minerals studied. Methods of mounting polished sections were investigated, and microhardness values of softer minerals have been shown to be appreciably affected by the stresses involved in thermoplastic methods. Cold-setting plastic mounting media were used in the present studies. The microhardness values were found to be strongly dependent upon
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