AMPHIBOLE

Photo shows a hornblende, the most abundant variety of amphibole.

Chemical Composition: X2Y5Si8O22(OH)2 where X=Ca, Na; Y=Mg, Fe, Al

Hardness: 5-6

Color: dark green to black (horneblende); green (actinolite); white (tremolite)

Specific Gravity: 2.9-3.8

Cleavage Planes: two; intersecting at 56 degrees and 124 degrees

Crystal Structure: long, six-sided crystals

Luster: nonmetallic

Other Properties: common in metamorphic and igneous rocks