Butlerite

Formula:  Fe(SO₄)(OH) ^. 2H₂O

Origin of name:  For Gurdon Butler, American geologist

Crystal system:  Monoclinic

Crystal class:  2/m

Twinning:

Unit cell: a = 6.51 Ǻ, b = 7.38 Ǻ, c = 5.86 Ǻ, β = 108.9°

Colour:  Orange to dark orange

Diaphaneity:

Luster:  Vitreous

Habit:  Crystals thick tabular or octahedral

Hardness:  2.5

Specific gravity:  2.55

Cleavage:  1; {100} perfect

Tenacity:

Streak:  Pale yellow

Synonyms/varieties:

Comments:  Dimorphous with parabutlerite