Tolbachite

Formula: CuCl₂

Origin of name: after locality Mount Tolbachik, Kamchatka, Russia

Crystal system: Monoclinic

Crystal class: 2/m

Twinning:

Unit cell: a = 6.89, b = 3.31, c = 6.82, β = 122.3°

Colour: Brown to gold-brown

Diaphaneity: Opaque to translucent

Luster: Pearly

Habit: crystals elongated, to 2 mm, forms fibrous moss-like growths encrusting basalt

Hardness: 

Specific gravity: 3.42

Cleavage: 1; {001} perfect

Tenacity: 

Streak: 

Synonyms/varieties:

Comments: hydrates on exposure (hygroscopic) becoming eriochalcite in air. Readily soluble in cold water. Found in fumaroles associated with melanothallite.