WATER IN NOMINALLLY ANHYDROUS CRUSTAL MINERALS: SPECIATION, CONCENTRATION, AND GEOLOGIC SIGNIFICANCE

Abstract

Why should we be interested in trace hydrous species in nominally anhydrous minerals in the Earth’s crust? After all, hydrous minerals dominate the pedosphere and are abundant to fairly common trace minerals in many metamorphic and igneous crustal rocks. On the other hand, the most abundant minerals in the crust—feldspars, quartz, pyroxenes, and garnet—are all nominally anhydrous. They are present even in systems with low total volatiles or fluid contents, or environments with low water activities where hydrous minerals are unstable. These nominally anhydrous minerals provide an opportunity to expand the extent of our knowledge of fluid composition and water activity, as well as the influence of water on physical properties and geochemical signatures of rocks.