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16.56: Prehnite

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    6281

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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  

    File:Prehnite2.jpg

    Figure \(\PageIndex{1}\): Prehnite cabochon
    Photo courtesy of Barbra Voltaire

     

    File:Prehnite1.jpg

    Figure \(\PageIndex{2}\): Prehnite crystals
    Photo courtesy of Barbra Voltaire