Amesite

Formula:  Mg₂Al(SiAl)O₅(OH)₄

Origin of name:  For James Ames, mine owner

Crystal system:  Triclinic, pseudo-hexagonal

Crystal class:  6/m 2/m 2/m

Twinning: common as six-fold sector twins on {001} and polysynthetic twins parallel to {010} prism edges

Unit cell: a = 5.307 Å, b = 9.195 Å, c = 14.068 Å, a = 90.09°, b = 90.25°, g = 89.96°

Colour:  Pale green, white

Diaphaneity: Translucent

Luster:  Pearly on cleavage

Habit:  Crystals prismatic or as pseudo-hexagonal plates; foliated aggregates

Hardness:  2.5 to 3

Specific gravity:  2.78

Cleavage: 1; {001} perfect

Tenacity: Brittle

Streak:  White with pale green tint

Synonyms/varieties:

Comments:  Data are for amesite-2H; there is also a 6R polytype. Member of the kaolinite-serpentine group. Formed as a product of low-grade metamorphism of Al, Mg-rich rocks.