Alunogen

Formula:  Al₂(SO₄)₃^.17H₂O

Origin of name:  From Latin for alum and from Greek genos for spawn or origin

Crystal system:  Triclinic

Crystal class:  -1

Twinning:

Unit cell: a = 7.42 Å, b = 26.97 Å, c = 6.062 Å, a = 89.95°, b = 97.566°, g = 91.888°

Colour:  Crystals colourless; aggregates white, yellowish, reddish

Diaphaneity: Transparent to translucent

Luster:  Vitreous, aggregates vitreous to silky

Habit:  Crystals prismatic with a six-sided outline, small and rare; usually as an efflorescence or fibrous crusts

Hardness:  1.5 to 2

Specific gravity:  1.77

Cleavage:  1; {010} perfect

Tenacity:

Streak: White

Synonyms/varieties:

Comments:  Soluble in water; crystals transparent; aggregates translucent