Hörnesite

Formula:  Mg₃(AsO₄)₂ ^. 8H₂O

Origin of name:   For Moritz Hörnes, Austrian mineral curator

Crystal system:  Monoclinic

Crystal class:  2/m

Twinning: 

Unit cell: a = 10.26, b = 13.44, c = 4.74, β = 104.9°

Colour:  White

Diaphaneity:  Transparent

Luster:  Pearly on cleavage

Habit:  Crystals prismatic, elongated on c axis, flattened, columnar, foliated

Hardness:  1

Specific gravity:  2.57

Cleavage:  2; {010} good, {100} poor

Tenacity: 

Streak: 

Synonyms/varieties: Hoernesite

Comments:  Series with erythrite