The Probert Encyclopaedia of Rocks & Minerals

AMPHIBOLE

The amphiboles are a large group of minerals, the silicates of many different bases, the commonest being alumina, iron oxide, lime, magnesia and the alkalis. They are constituents of many crystalline igneous rocks and of metamorphic schists. In many of their properties they closely resemble the pyroxenes. They occur generally in black or dark green crystals, usually long, narrow and blade-like, and owing to their perfect cleavages their surfaces are smooth and bright. The commoner varieties are hornblende, actinolite and tremolite.
Research Amphibole