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Prehnite (Photo) [abbr. Prh ]

Year of discovery: 1788 (Karoo dolerites, South Africa), 1893 (Japan)

Locality list: 357 localities of prehnite

• Ca₂Al₂Si₃O₁₀(OH)₂
• [Ca²⁺₂][Al³⁺][(OH)₂|AlSi₃O₁₀]^7-

• Class: Aluminosilicate (Ino-Phyllo transitional) - Hydroxide
• Soluble in: HCl (Decompose)
• Fluorescence: UV excitation (Pale blue-Yellow)

• Al => Fe3+: Ferriprehnite

• Color: Colorless, Gray, Yellowish green
• Streak: White
• Luster: Vitreous
• Diaphaneity: Translucent

• Habit: Platy
• Aggregate: Reniform

• Cleavage: Good on {001} (1 plane), Poor on {110} (2 planes)
• Hardness: 6-6.5
• Density: 2.9

• System: Orthorhombic
• Group: mm2, P2cm
• Lattice: a=4.6, b=5.5, c=18.5

Etymology: H. Von Prehn (1733-1785), Dutch Colonel