Picromerite

Formula: K₂Mg(SO₄)₂.6H₂O

Origin of name: from Greek for bitter and part, in allusion to the magnesium content which makes this water-soluble salt bitter to the taste.

Crystal system: Monoclinic

Crystal class: 2/m

Twinning: 

Unit cell: a = 9.064, b = 12.256, c = 6.113, Z = 2; beta = 104.8°

Colour: Colourless, white, gray, yellowish or reddish from impurities

Diaphaneity: Transparent

Luster: Vitreous

Habit: Crystals short prismatic, crusts or massive

Hardness: 2.5

Specific gravity: 2.028 (synthetic)

Cleavage: 1; {201} perfect (synthetic)

Tenacity: 

Streak: White

Synonyms/varieties: Schönite, schoenite

Comments: Easily soluble in water