Lawsonite

Formula:  CaAl₂Si₂O₇(OH)₂ ^. H₂O

Origin of name:  For A. Lawson, Scottish - American geologist

Crystal system:  Orthorhombic

Crystal class:  2/m 2/m 2/m

Twinning:  Lamellar on {101}

Unit cell: a = 8.788 Ǻ, b = 13.13 Ǻ, c = 5.846 Ǻ

Colour:  Colourless, white, gray, blue, pinkish

Diaphaneity: 

Luster:  Vitreous to greasy

Habit:  Crystals prismatic or tabular; subhedral tablets; massive, granular

Hardness:  6

Specific gravity:  3.05 to 3.12

Cleavage:  3; {100} and {010} perfect, {101} imperfect

Tenacity:  Brittle

Streak:  White

Synonyms/varieties:

Comments:  Dimorphous with partheite