Talmessite

Formula: Ca₂Mg(AsO₄)₂.2H₂O

Origin of name: after locality Talmessi mine, Iran

Crystal system: Triclinic

Crystal class: 1

Twinning:

Unit cell: a = 5.89, b = 7.69, c = 5.56, α = 112.633°, β = 70.817°, γ = 119.417°

Colour: Colourless, white, pale green (nickelian), brownish pink (cobaltian)

Diaphaneity: Transparent to translucent

Luster: Vitreous

Habit: crystals minute, in druses and fine-crystalline aggregates, may be stalactitic or in crusts

Hardness: 5 (by analogy to the fairfieldite group)

Specific gravity: 3.2 to 3.5

Cleavage: None

Tenacity: 

Streak: White

Synonyms/varieties:

Comments: series with gaitite