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Piemontite (Photo) [abbr. Pmt ]

Year of discovery: 1758 (Prabornaz mine, Italy), 1887 (Japan)

Locality list: 182 localities of piemontite

• Ca₂MnAl₂(SiO₄)₃(OH)
• Ca₂(Al,Mn,Fe)₃(SiO₄)₃(OH)
• [Ca²⁺₂][Mn³⁺][Al³⁺₂][OH|O|SiO₄|Si₂O₇]^13-

• Class: Epidote group < Epidote supergroup
• Class: Sorosilicate - Nesosilicate - Oxide - Hydroxide

• Ca => Sr: Piemontite-(Sr)
• Ca => Pb: Piemontite-(Pb)

• Mn => Al: Zoisite, Clinozoisite
• Mn => Fe: Epidote
• Mn => V: Mukhinite

• Color: Red, Dark red
• Streak: Red
• Luster: Vitreous
• Diaphaneity: Translucent-Opaque

• Habit: Prismatic

• Cleavage: Perfect on {001} (1 plane), Poor on {100} (1 plane)
• Hardness: 6-6.5
• Density: 3.5

• System: Monoclinic
• Group: 2/m, P2₁/m
• Lattice: a=8.9, b=5.7, c=10.2, β=115.3