Formula: (Na,K)FeFeSi6O15
Origin of name: after locality Opo Bay, Mayor (Tuhua) Island, New Zealand
Crystal system: orthorhombic
Crystal class: 2/m 2/m 2/m
Twinning:
Unit cell: a = 14.31 Å, b = 17.28 Å, c = 10.11 Å
Colour: dark blue to black
Diaphaneity:
Luster:
Habit: crystals prismatic
Hardness: 3 to 4
Specific gravity: 2.89
Cleavage: 3; {100}, {010} and {001} good
Tenacity: brittle
Streak:
Synonyms/varieties:
Comments:
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