PLEASE DO NOT DESTROY OR THROW AWAY THIS PUBLICATION. If you haw no further use for it, write to the Geological Survey at Washington and ask for a frank to return it UNITED STATES DEPARTMENT OF THE INTERIOR Harold L. Ickes, Secretary GEOLOGICAL SURVEY W. C. Mendenhall, Director Bulletin 848 THE MICROSCOPIC DETERMINATION OF THE NONOPAQUE MINERALS SECOND EDITION BY ESPER S. LARSEN AND HARRY HERMAN UNITED STATES GOVERNMENT PRINTING OFFICE WASHINGTON : 1934 For sale by the Superintendent of Documents, Washington, D. C. ------ Price 20 cents CONTENTS " '*" ^ t**v Page 1'f) OHAPTER 1. Introduction_______-____-----------_---------.-----_-_ 1 The immersion method of identifying minerals.______--___-_-___-_ 1 New data._______-___________-__-_-________-----_--_-_---_-_- 2 Need of further data.________------------------------------_-- 2 ; Advantages of the immersion method..___-__-_-__-_---__________ 2 Other suggested uses for the method___________________________ 3 Work and acknowledgments.___________-_____-_---__-__-___-___ 3 CHAPTER 2. Methods of determining the optical constants of minerals. __ 5 The chief optical constants and their interrelations________________ 5 Measurement of-indices of refraction____---____-__-_--_--_-_____ 8 The embedding method..___--------_-___-_-_-__--__-______ 8 The method of oblique illumination.___._-_-______-_____ 9 The method of central illumination______________________ 10 Dispersion method.----------------------.------------ 10 : Immersion media______--_---_-----_---------------------- 11 General features.--.-.-------------------------------- 11 Piperine and iodides.---.------------.----------------- 13 Sulphur-selenium melts_----------------------------_ 15 Selenium and arsenic selenide melts._____--_--_----_-___ 17 Halogens of thallium-___---_---_-_-------------------- 17 Methods of standardizing media for measuring indices of refraction.___________----__-_-_-_-----------------_ 18 Measurement of all indices of refraction of crystals.___________ 20 Measurements of axial angles.-.--------------------------.----- 22 Dispersion of the optic axes______----------------------------_- 23 Optical character..____________-_-______--_-_-_ ---___---___ 24 Optical orientation, dispersion of bisectrices, and crystal system..... 24 Dispersion of the indices of refraction______ ________________ 27 Other tests..-.___________--_.________------------- 27 CHAPTER 3. Some statistics on the optical properties of minerals. _______ 28 Distribution of minerals with regard to optical character.__________ 28 Distribution of minerals with regard to index of refraction and bi­ refringence _______________-___-----_-___-_---------_----___- 28 Relation between index of refraction, density, and chemical compo- sition________-__-._______.__.-_-_-___- -__-_-_-_-_--____ 30 CHAPTER 4. Tables for the determination of minerals from their optical properties._____________________________________________________ 33 Arrangement of the data in the tables.__________________________ 33 Completeness of the data.--.--------------------.-------------- 34 Tables._____________-___-_-____________________ 35 List of minerals arranged according to their intermediate indices of refraction, j8, and showing their birefringences-___________ 35 Data for the determination of the nonopaque minerals...--. 47 Isotropic group.-------------------------------------- 47 Uniaxial positive group-_--_--------------_---_-------_ 67 m IV CONTENTS Page CHAPTER 4. Tables for the determination of minerals from their optical properties Continued. Tables Continued. Data for the determination of the nonopaque minerals Contd. Uniaxial negative group______________________________ 77 Biaxial positive group.__-_---___--_______--____-____-- 95 Biaxial negative group.._______________________________ 148 Minerals of unknown optical character.__________________ 213 Data on mineral groups..______________________________________ 219 Alunite group.____________________________________________ 219 Amphibole group_____._____.__________________________ __ 219 Apatite group.___________________________________________ 228 Aragonite group._____________________________:___________ 228 Barite group___._---__.---_---_-__-_-____..___---_-_-_____ 229 Calcite group....,.-_______________________________________ 229 Chlorite group__----_--_-_--_----______-_____-__--------_. 230 Epidote group..__________________________________________ 231 Feldspar group.____-_.-_-._-_-___-_-_--_--____-----_------_ 233 Garnet group._________-__-________:.___-_____-_-___-_---- 233 Melilite group. ___________________________________________ 235 Mica group.________-___-_---_-_________-____--_-____--. 236 Olivine group_________________---_-____-______-__-_____-__ 239 Pyroxene group.._________________________________________ 240 Scapolite group.___-______-_________.________-_------_---_ 245 Spinel group______---_____--__-__._-_-_-___------------. 246 Tourmaline group.._______________________________________ 247 Uranite group.___________________________________________ 247 Vivianite group.__________________________________________ 248 The zeolites..-------------------------------------------. 250 INDEX ______----------_-----------_--_-_----_----_-_-----------_- 255 ILLUSTRATIONS Page FIGURE 1. The error in V'a as computed from the approximate formula Cos' V'a = 7^________-______---- a _____,-__-___-___ 7 2. Indices of refraction of mixtures of piperine and iodides_____ 14 3. Indices of refraction of mixtures of sulphur and selenium..-- 16 4. Brass frame for prism for determination of the refractive indices of liquids._._-_------_-_-_---_----_-_--_...... 19 5. Stereographic projection of the optical elements of a triclinic mineral (axinite)..____----_-_----_----_---__--_-_---_ 26 6. Diagram showing density of distribution of the nonopaque minerals with respect to the intermediate index of refraction. 29 7. Diagram showing density of distribution of the nonopaque minerals with respect to index of refraction and birefrin­ gence __--_----_-----_----_--_------_---------__-____ 29 V NOTE TO THE SECOND EDITION In this second edition of the bulletin on the microscopic determination of the nonopaque minerals (U. S. Geological Survey Bulletin 679) the first three chapters have been left, essentially as they were in the first edition; the fourth chapter of the first edition, which contained the new data, has been omitted, as a single publication of these data seemed sufficient; and the fifth chapter of the first edition becomes the fourth in the new edition. The tables, for the determination of minerals from their optical properties have been brought up to date by more than 500 new entries and 100 changes in old entries. About 250 new species and old species not given in the previous edition are included. Of these new data about 80 entries represent measurements made by the authors. Such data are indicated in the tables by an asterisk (*). At the recommendation of several mineralogists, tables have been added assembling the data of some of the mineral groups, including the alunite, am- phibole, apatite, aragonite, barite, calcite, chlorite, epidote, feldspar, garnet, melilite, mica, olivine, pyroxene, scapolite, spinel, tourmaline, vivianite, and uranite groups and the zeolites. Other new features of this edition are the addition of a column in the main table to indicate the variability of the indices of refraction and other data given for the mineral, and the addition of the calculations of 2E immediately below 2V. VI THE MICROSCOPIC DETERMINATION OF THE NONOPAQUE MINERALS SECOND EDITION By ESPER S. LARSEN and HARRY BERMAN CHAPTER 1. INTRODUCTION THE IMMERSION METHOD OF IDENTIFYING MINERALS Optical methods of determining minerals with the petrographic microscope have long been used and have been carried to a high state of development in studies of the minerals in thin sections of rocks and ores, yet out of about 1,000 mineral species comparatively few can be identified readily in thin sections. A mineral whose optical properties are known can be accurately and quickly identi­ fied, however, by the immersion method that is, by immersing its powder in liquid media whose indices of refraction are known and determining its optical constants. In this bulletin the authors give a set of tables for the systematic determination of minerals from their optical constants, describe briefly some methods for the rapid deter­ mination of optical constants, give the results of measurements of the optical constants of more than 500 species for which data were not previously available prior to the first edition, and present sta­ tistics on the optical properties of minerals. The first tables prepared for general use in determinations of minerals by the immersion method were those of Van der Kolk,1 published in 1900. Somewhat similar tables, prepared by A. F. Rogers,2 were published in 1906, and an optical mineralogy contain­ ing tables and description of all minerals for which optical data were then available, prepared by N. H. and A. N. Winchell,3 was published in 1909. 1 Schroeder van der Kolk, J. O., Tabellen zur mikroskopischen Bestlmmung der Mineralien nach ihrem Brechungsindex, Wiesbaden, 1000; 2d ed., revised and enlarged by E. H. M. Beekman, 1006. ' Rogers, A. F., School of Mines Quart., vol. 27, pp. 340-350,1006. * Winchell, N. H. and A. N., Elements of optical mineralogy, D. Van Nostrand Co., 1000. 2 MICROSCOPIC DETERMINATION OF NONOPAQUE MINERALS NEW DATA In attempting to employ the immersion method some years age* the senior author