Excerpt from The Data of Geochemistry In the crust of the earth, with its liquid and gaseous envelopes, the ocean and the atmosphere, about eighty chemical elements are now recognized. These elements, the primary units of chemical analysis, are widely different as regards frequency; some are extremely rare, others are exceedingly abundant. A few occur in nature uncombined but most of them are found only in combination. The compounds thus generated, the secondary units of geochemistry, are known as mineral species; and of these, excluding substances of organic origin, only about a thousand have yet been identified. By artificial means innumerable compounds can be formed; but in the chemistry of the earth's crust the range of possibility seems to be extremely limited. From time to time new elements and new mineral species are discovered; but it is more than probable that all of them which have any large importance in the economy of nature are already known. The rarest substances, however, whether elementary or com pound, supply data for the solution of chemical problems; they can not, therefore, be ignored or set to one side as having no significance. In scientific investigation all evidence is of value. 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.