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amphibole
Any of a large group of rock-forming, hydrated metasilicate minerals. Amphiboles have a structure of silicate tetrahedra linked to form double endless chains, in contrast to the single chain of pyroxenes, to which they are closely related. Present in many igneous and metamorphic rocks, amphiboles are generally dark-colored and contain various combinations of sodium, calcium, magnesium, and aluminum.
The most important minerals in this group are tremolite, actinolite, nephrite (jade), and hornblende. Asbestos and its varieties are forms of tremolite and actinolite. Many of these occur as fine hair-like filaments, readily separable from each other; in other cases, the filaments or fibers are more or less firmly interwoven.
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