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A green to black mineral composed of calcium-magnesium silicate. Actinolite mixed with tremolite forms Nephrite, a translucent green mineral that is one of the forms of Jade. Actinolite deposits occur in Great Britain, Russia, Japan, China, Austalia, Brazil, Canada (British Columbia), and the U.S. (Alaska, California, Wyoming and Vermont). The transparent to opaque stone is used as a filler in paints and ceramics.

Synonyms and Related Terms


Physical and Chemical Properties

  • Monoclinic system with fibrous or granular crystalline masses.
  • Luster = vitreous to silky.
  • Streak = colorless
  • Cleavage is perfect in two directions; fracture is splintery
Composition Ca2(MgFe)5Si8O22(OH)2
Mohs Hardness 5.0-6.0
Density 3.0-3.2 g/ml
Refractive Index 1.60-1.64

Resources and Citations

  • C.W.Chesterman, K.E.Lowe, Audubon Society Field Guide to North American Rocks and Minerals, Alfred A. Knopf, New York, 1979
  • actinolite (accessed Sept. 2007); sp. grav.=3.03-3.24; streak=white; cleavage=good in one direction

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