Colourless to green amphibole mineral, darkening with increased iron content from green to black. It has a prismatic and splintery texture and is abundant in regionally metamorphosed (see metamorphism) rocks such as schists. Actinolite has a monoclinic crystal structure, and it may alter to chlorite. See also asbestos.

This entry comes from Encyclopædia Britannica Concise.
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