Formula: Ca2(Al,Mn,Fe)3(SiO4)3(OH)
Origin of name: after locality Piemonte, Italy
Crystal system: monoclinic
Crystal class: 2/m
Twinning:
Unit cell: a = 8.84 Å, b = 5.67 Å, c = 10.15 Å, b = 115.3°
Colour: reddish brown to reddish black, purplish red
Diaphaneity:
Luster: vitreous
Habit: crystals prismatic or acicular, massive, coarse to fine granular, fibrous
Hardness: 6
Specific gravity: 3.45 to 3.52
Cleavage: 1; {001} perfect
Tenacity: uneven, brittle
Streak: reddish
Synonyms/varieties: manganepidote, piedmontite
Comments:
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