Stilbite
Lonavla, India

This specimen measures 10cm x 19cm with individual bowties measuring 5cm in length

Stilbite NaCa₂Al₅Si₁₃O₃₆^.16H₂O

Tectosilicate; hydrous calcium, sodium, aluminum silicate; zeolite group

Color and Luster: White, grayish, yellowish, red to brown; vitreous, pearly on cleavage; streak colorless

Hardness: 3.5-4

Cleavage: Perfect, one direction

Fracture: Uneven

Crystals: Monoclinic; commonly in bladed aggregates of numerous twinned crystals, pinched in the middle to resemble wheat sheaves; also radial, globular, rarely as tabular crystals

Photo by Mary Sutherland

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