Formula: (Mg,Fe)Al3(BO4)(SiO4)O
Origin of name: For A. Grandidier, French explorer
Crystal system: Orthorhombic
Crystal class: 2/m 2/m 2/m
Twinning:
Unit cell: a = 10.34, b = 10.98, c = 5.76
Colour: Bluish green, greenish blue
Diaphaneity: Translucent to transparent
Luster: Vitreous
Habit: Crystals elongated, indistinct, tabular
Hardness: 7.5
Specific gravity: 2.98
Cleavage: 2; {100} perfect, {010} distinct
Tenacity: Brittle, uneven
Streak: White
Synonyms/varieties:
Comments:
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