Laumontite

Formula:  CaAl₂Si₄O₁₂ ^. 4H₂O

Origin of name:  For F. de Laumont, French discoverer of mineral

Crystal system:  Monoclinic

Crystal class:  2/m

Twinning:  On {100}, contact (swallow-tail)

Unit cell: a = 14.76 Ǻ, b = 13.08 Ǻ, c = 7.56 Ǻ, β = 112.0°

Colour:   White, gray, yellowish, pink, brownish

Diaphaneity: 

Luster:  Vitreous to pearly

Habit:  Crystals square prisms with steep oblique terminations; fibrous, columnar, radiating and divergent

Hardness:  3 to 4

Specific gravity:  2.20 to 2.41

Cleavage:  2; {010} and {110} perfect

Tenacity:  Uneven

Streak:  Colourless

Synonyms/varieties:  Leonhardite (partially dehydrated var.)

Comments:  Readily loses water on exposure and crumbles