Aluminotschermakite

Formula:  Ca₂(Mg,Fe)₃(Al,Fe)₂(Si₆Al₂)O₂₂(OH)₂

Origin of name:  From aluminum and tschermakite

Crystal system:  Monoclinic

Crystal class:  2/m

Twinning: Simple or multiple parallel {100}

Unit cell: a = 9.76 Å, b = 17.99 Å, c = 5.33 Å, b = 105.10°

Colour:  Green

Diaphaneity: Translucent

Luster: Vitreous

Habit: prismatic crystals, as reaction rims on other minerals

Hardness:  5 to 6

Specific gravity:  3.13

Cleavage: 3; {110} perfect, {100} and {001} parting

Tenacity: Brittle

Streak:

Synonyms/varieties:

Comments:  Series with ferrotschermakite and with tschermakite. Member of the amphibole group. Found in eclogites and other ultramafic igneous rocks; in medium- to high-grade metamorphic rocks, typically amphibolites.