Abstract
THE identification of a mineral fragment by means of the micrscope, to be beyond doubt, must be based upon some quantitative test, such as a measurement of the refractive indices, or, in the case of doubly refractive substances, the amount of double refraction and the-relation of the extinction directions to the crystalline form, or, in that of biaxial substances, a measurement of the angle between the optic axes. Recent years have witnessed great progress in the discovery of more convenient or more accurate methods of effecting such measurements, and almost equal progress in the design of the instruments and accessory apparatus. So rapid has been the advance that it has outpaced the text-books. Petrologists and all who may have occasion to identify minerals from chance fragments will therefore feel grateful to Dr. F. E. Wright tor the admirable treatise in which he describes in detail and discusses with critical acumen the various methods and devices available. Dr. Wright is himself responsible for no mean share in the progress that has been made, and it is an excellent feature of the volume that he is in a position to write of almost every method or piece of apparatus from first-hand experience in the Geophysical Laboratory; the pages, in fact, teem with those practical hints and suggestions which prove so useful to the worker.
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The Microscopic Determination of Minerals 1 . Nature 89, 673–674 (1912). https://doi.org/10.1038/089673a0
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DOI: https://doi.org/10.1038/089673a0