Prehnite

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Prehnite
Chemical composition Ca2Al2Si3O10(OH)2+Fe
Crystal system Orthorhombic
Habit Usually Fibrous Aggregate
Cleavage Good:1 direction
Fracture Uneven-Conchoidal
Hardness 6-6.5
Optic nature Biaxial (+) Aggregate
Refractive index 1.649-1.616
Birefringence .020-0.031
Specific gravity 2.90
Lustre Vitreous-Pearly

Prehnite

Prehnite cabochon
Photo courtesy of Barbra Voltaire
Prehnite crystals
Photo courtesy of Barbra Voltaire