Armenite

Formula:  BaCa₂Al₆Si₉O₃₀^.2H₂O

Origin of name:  From locality; Armen mine, Kongsberg Norway

Crystal system:  Orthorhombic

Crystal class:  2/m 2/m 2/m

Twinning: complex, showing sectored triplets, may be lamellar

Unit cell:   a = 13.87 Å, b = 18.66 Å, c = 10.70 Å

Colour:  Grayish green, colourless

Diaphaneity: Translucent

Luster:  Vitreous

Habit:  Crystals prismatic

Hardness:  7.5

Specific gravity:  2.75

Cleavage:  2; {010} perfect, {110} distinct

Tenacity:  Brittle

Streak: White

Synonyms/varieties:  Calciocelsian

Comments: Might be a member of the milarite group (?). Found in calcite veins; in manganese-metasomatised diorite included in later granodiorite.