Minerals and the Microscope Book

H. G. SMITH MINERALS and the MICROSCOPE Completely Revised by M. K. M. SC., PH. D. University College, London London Thomas Murby Co FOURTH EDITION 1956 REPRINTED 1957 This book is copyright under the Berne Convention. Apart from any fair dealing for the purposes of private study research, criticism or review, as per mitted under the Copyright Act 1956, no portion may be reproduced by any process without written permission. Enquiry should be made to the publisher. George Allen and Unwm Ltd. 1914 George Allen Unwm Ltd. 40 Museum Street, London, W. C. I TOre now the proprietors of Thomas Murbv Co. Printed in Great Britain , in 10 11 Times Roman by The Black friars Press Ltd. Leicester PREFACE TO FOURTH EDITION The late H. G. Smith succeeded to a notable degree in providing several generations of students of Geology with a concise and understandable introduction to the study of minerals in thin sections under the microscope. The present writer has tried to keep the subject matter within the bounds of previous editions, but some expansion has been necessary. Much of the book has been re-written, partly because of changes in the design of petrological micro scopes, partly as a consequence of the growth of knowledge on the subject. Formerly the polarising apparatus below the stage of the microscope was easily removed from the light-path, and it was therefore appropriate in earlier editions to include a chapter on the appearance of thin sections of minerals in ordinary non-polarised light. In most modern instruments, however, the polariser is used as a fixture polarised light is invariably used in the study of thin rock-and mineral sections, and such a chapter becomes unnecessary. The writer believes that a good working knowledge of all the apparatus used is essential in the training of the geological student. Therefore the one-page description of the petrological microscope of former editions has been expanded, so that the beginner may make the most efficient use of the instrument which is a precision instrument at his disposal. For similar reasons the specialised techniques used in the study of sections of minerals are rather more fully described and explained than formerly. The most important development in mineralogy within recent times has been the application of X-ray techniques to the study of the internal structure and detailed composi tion of minerals. As a result it is now practicable and desirable to discuss the composition of, say, the all important rock-forming silicates in terms which can be understood by everybody. A section dealing with this aspect of mineralogy has therefore been included in the new edition. In the description of each mineral a short paragraph has been devoted to modes of occurrence, as essential back ground knowledge the associations of minerals are as important as their specific properties. The thirty-page introduction to petrology found in pre vious editions has been deleted, as it is considered out of context in a book with the title, Minerals and the Microscope. The writer is grateful to his father, Dr. A. K. Wells, for criticism and help in the preparation of the new edition, and also to his colleagues at University College, London, for assistance rendered. August, 1955. MAURICE K. WELLS. CONTENTS CHAPTER PAGE PREFACE TO FOURTH EDITION 1 Introduction . . . . . . . . 1 2 The Petrological Microscope . . 5 3 Some Principles of Refraction and Double Refraction in Minerals . . 13 4 The Examination of Minerals with Ordinary and Plane Polarised Light 25 5 The Examination of Minerals between Crossed Polarisers . . 38 6 Use of the Microscope Accessories and Observations in Convergent Light 5 1 7 The Nature of Rock-forming Minerals . . . . . . . 73 8 The Ferro-Magnesian Silicates The Olivine Group SI The Pyroxene Group 83 The Amphibole Group 91 The Mica Group 95 The Chlorite-Serpentine Group ...Read More