Amphibole

Noun

Any member of a large group of hydrated double silicate minerals which are structurally similar and usually dark (green to black, but may be colorless, white, yellow, blue, or brown). Amphiboles are generally composed of a silicate bonded to various metal ions, such as aluminum, calcium, iron, magnesium, or sodium (usually magnesium-iron with the other metals in varying amounts). These minerals occur as fibrous prismatic or columnar crystals in igneous and metamorphic rocks. Some amphiboles are orthorhombic, but most are monoclinic. Some examples of amphiboles are actinolite, anthophyllite, asbestos, cummingtonite, glaucophane, horneblende, riebeckite, and tremolite. A form of jade known as nephrite consists of actinolite in finely fibrous form.

Chemical Formula: (Mg,Fe,Ca,Na)_2-3(Mg,Fe,Al)₅(Si,Al)₈O₂₂OH₂

External Links

• Amphibole - Wikipedia