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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