Prehnite and Epidote
Loudoun County, Virginia

This specimen measures 12cm x 6.5cm

Epidote Ca₂Al₂FeOSiO₄Si₂O₇(OH)

Sorosilicates; basic calcium, aluminum, iron silicate

Color and Luster: Yellowish green to brownish black; vitreous; streak colorless to gray

Hardness: 6-7

Cleavage: Perfect, one direction lengthwise

Fracture: Uneven, brittle

Crystals: Monoclinic; usually in long, slender, grooved prismatic crystals that are frequently terminated by two sloping faces; also thick tabular crystals; massive, columnar, divergent, acicular, granular

Prehnite Ca₂Al₂Si₃O₁₀(OH)₂

Complex silicate; calcium aluminum silicate, often with some iron

Color and Luster: Light green, oil-green, gray, white, colorless; frequently fading upon exposure; vitreous, waxy; streak colorless

Hardness: 6-6.5

Cleavage: Distinct, one direction

Fracture: Uneven

Crystals: Orthorhombic; crystals rare, usually in botryoidal masses, withridged surfaces marked by edges of curving crystals; also stalactitic, radial fibrous

Photo by Mary Sutherland

Descriptions taken from
The Audubon Society Field Guide to North American Rocks and Minerals