Brandtite

Formula:  Ca₂(Mn,Mg)(AsO₄)₂ ^. 2H₂O

Origin of name:  For G. Brandt, Swedish chemist

Crystal system:  Monoclinic

Crystal class:  2/m

Twinning:  Common on {100}

Unit cell: a = 5.90 Ǻ, b = 12.97 Ǻ, c = 5.68 Ǻ, β = 108.1°

Colour:  Colourless to white

Diaphaneity:

Luster:  Vitreous

Habit:  Crystals microscopic, slender prismatic or stout prismatic; radial groups and rounded or reniform masses

Hardness:  3.5

Specific gravity:  3.67

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

Tenacity:

Streak:

Synonyms/varieties:

Comments:  Dimorphous with parabrandtite