Natrolite

Formula: Na₂Al₂Si₃O₁₀.2H₂O

Origin of name: from Latin natrium = sodium

Crystal system: orthorhombic

Crystal class: mm2

Twinning: on {110}, {011} or {031}

Unit cell: a = 18.28 Å, b = 18.62 Å, c = 6.592 Å

Colour: colourless, white, gray, yellowish, reddish

Diaphaneity: 

Luster: vitreous to somewhat pearly

Habit: crystals prismatic, short or long slender to acicular, striated vertically, massive, granular or compact, fibrous, radiating

Hardness: 5 to 5.5

Specific gravity: 2.20 to 2.26

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

Tenacity: uneven, brittle

Streak: 

Synonyms/varieties:

Comments: dimorphous with tetranatrolite, member of the zeolite group