Prehnite
Prospect Park, Patterson, New Jersey

The specimen is 25 cm. wide and 18 cm. high. It is from Prospect Park, Paterson, New Jersey, where it formed relatively early in the pocket paragenesis of pillow basalts, from the Triassic-age Watchung Mountains. The specimen was acquired for the collection from Jim's Gems in 1979.

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, with ridged surfaces marked by edges of curving crystals; also stalactitic, radial fibrous

Prehnite is commonly found in cavities and "pillows" and along fractures of basalt and diabase rock and in association with quartz, datolite, appophyllite, and various minerals of the zeolite group. While it has an interest to mineral collectors, there is presently no economic value for this mineral.

Photo by Mary Sutherland

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