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Bannisterite (Photo)

Year of discovery: 1936 (Benallt mine (Tyddyn Meirion mine), UK, and Franklin mine, USA), 1968 (Japan)

Locality list: 8 localities of bannisterite

• K_0.5Ca_0.5Mn₁₀(Si,Al)₁₆O₃₈(OH)₈,5.5H₂O
• (K,Na)_0.5Ca_0.5(Mn,Fe)₁₀(Si,Al)₁₆O₃₈(OH)₈,5.5H₂O
• [K⁺_0.5][Ca²⁺_0.5][Mn²⁺₁₀][(OH)₈|(Si,Al)₁₆O₃₈]^21.5-,5.5H₂O

• Class: 2:1 layer, Other Tetrahedral < Modulated hydrous < Phyllosilicate subclass < Silicate class
• Class: Phyllo-Aluminosilicate - Hydroxide - Hydrate
• Radioactive: Very weak

• Color: Brown
• Streak: Pale brown
• Luster: Resinous
• Diaphaneity: Translucent

• Habit: Foliate

• Cleavage: Perfect on {001} (1 plane), Distinct (1 plane)
• Hardness: 4
• Density: 2.8

• System: Monoclinic
• Group: 2/m, A2/a
• Lattice: a=22.3, b=16.4, c=24.7, β=94.3