Langite

Formula:  Cu₄(SO₄)(OH)₆ ^. 2H₂O

Origin of name:  For V. von Lang, Austrian physicist

Crystal system:  Monoclinic

Crystal class:  m

Twinning:  Common on {110}, repeated

Unit cell: a = 6.02 Ǻ, b = 11.2 Ǻ, c = 7.12 Ǻ, β = 90.01°

Colour:  Greenish blue, sky-blue to bluish green

Diaphaneity: 

Luster:  Vitreous, crusts silky

Habit:  Crystals elongate or equant; scaly; crusts or earthy

Hardness:  2.5 to 3

Specific gravity:  3.31

Cleavage:  2; {001} perfect, {010} distinct

Tenacity: 

Streak: 

Synonyms/varieties:

Comments:  Dimorphous with wroewolfeite