Anthophyllite

Formula:  (Mg, Fe)₂(Mg, Fe)₅Si₈O₂₂(OH)₂

Origin of name:  From neo-Latin for clove (for its colour)

Crystal system:  Orthorhombic

Crystal class:  2/m 2/m 2/m

Twinning:

Unit cell:   a = 18.54 Å, b = 18.03 Å, c = 5.28 Å

Colour:  White, grey, greenish, brownish green, clove-brown, dark

Diaphaneity: Transparent to translucent

Luster:  Vitreous to silky

Habit:  Crystals prismatic, rare; massive, fibrous, or lamellar

Hardness:  5.5 to 6

Specific gravity:  2.9 to 3

Cleavage:  3; {210} perfect, {010} and {100} imperfect

Tenacity: Brittle, fibres are elastic

Streak:  Colourless or greyish

Synonyms/varieties:  Anthogrammite, antholite, anthophylline, schillerspath, strelite, thalackerite (metallic luster var.), picroamosite (Fe³⁺ rich var.), valleite

Comments:  Series with magnesio-anthophyllite and ferro-anthophyllite. Member of amphibole group. Formed during medium- to high-grade metamorphism, in amphibolites, gneisses, metaquartzites, iron formations, granulites, and schists derived from argillaceous sediments, ultramafic, or mafic igneous rocks; as retrograde reaction product.