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Actinolite crystals
Image credit: RRUFF


Green to black acicular to bladed crystals 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, Australia, Brazil, Canada (British Columbia), and the U.S. (Alaska, California, Wyoming and Vermont). It is often found in association with talc and chlorite. The transparent to opaque stone is used as a filler in paints and ceramics.

Synonyms and Related Terms

Raman spectrum
Image credit: RRUFF


Physical and Chemical Properties

  • Monoclinic system with fibrous crystalline masses
  • Luster = vitreous to silky
  • Streak = colorless
  • Cleavage = perfect in two directions
  • Fracture = splintery to granular
  • Fluorescence = inert
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