Excerpt from A Key for the Determination of Rock-Forming Minerals in Thin Sections Tables for the determination of minerals have heretofore been made of secondary importance in text books. In this volume the reverse method has been adopted and the de scriptive tables make up the greater portion of the book. Theoretical discussions in optics have been avoided so far as possible, and only enough has been given to make clear that which is necessary for the practical determination of the minerals. The material has been condensed as much as is consistent with clearness, and all of the descriptions are given in as concise a form as possible. Owing to the difficulty of having the pages of the index indented by machinery, it was found necessary to extend the leaves to the full width of the book, and to indicate the lines along which the student should cut the pages. After trim ming along the lines shown, it will be found convenient to form another index guide by cutting off about one-half inch from the upper right hand corners of the pages descriptive of negative minerals. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.