Beidellite

Formula:  (Na,Ca_0.5)_0.3 Al₂ (Si,Al)₄ O₁₀ (OH)₂ ^. nH₂O

Origin of name:  After locality; Beidell, Saguache, Colorado

Crystal system:  Monoclinic

Crystal class:  2/m

Twinning:

Unit cell: a = 5.179 Å, b = 8.970 Å, c = 17.57 Å (depending on water content in interlayer)

Colour:  White, reddish, brownish grey

Diaphaneity:

Luster:  Waxy to vitreous

Habit:  Crystals minute thin plates; clay-like masses

Hardness:  1 to 2

Specific gravity:  2 to 3

Cleavage:  1; {001} perfect

Tenacity:

Streak:

Synonyms/varieties:

Comments: Member of the smectite group. Found as a constituent of bentonite clays, as alteration product in hydrothermal mineral deposits, especially porphyry-Cu-Mo systems, in soils derived from mafic rocks.