Actinolite (Var. Byssolite)
Fairfax Quarry
Centreville, Virginia
This specimen measures 11cm x 6cm
Actinolite Ca2(Mg,Fe)5Si8O22(OH)2
Inosilicate; calcium, magnesium, iron silicate, amphibole group
Color and Luster: Bright to dark green, grayish green, black; vitreous, pearly, silky; streak colorless
Hardness:5-6
Cleavage: Perfect, two lengthwise directions form a diamond
Fracture: Splintery, uneven
Crystals: Monoclinic, often long prismatic with diamond shaped cross sections, also bladed, acicular(Var. byssolite), columnar, divergent
Photo by Mary Sutherland
Descriptions taken from
The Audubon Society Field Guide to North American Rocks and Minerals