Arthurite

Formula:  CuFe₂(AsO₄, PO₄,SO₄)₂(O,OH)₂^.4H₂O

Origin of name:  For Sir Arthur Edward Ian Montagu Russell (1878-1964) and Arthur William Gerald Kingsbury (1906-1968), British mineralogists

Crystal system: Monoclinic

Crystal class: 2/m

Twinning:

Unit cell: a = 10.189 Å, b = 9.649 Å, c = 5.598 Å, b = 92.16°

Colour:  Apple-green to emerald-green

Diaphaneity: Transparent to translucent

Luster:  Vitreous

Habit: Prismatic to acicular crystals, commonly as spherical aggregates and thin crusts

Hardness: 3-4

Specific gravity:  about 3.2

Cleavage: None

Tenacity:  Brittle

Streak: Light green

Synonyms/varieties:

Comments: Member of the arthurite group. Formed as a rare secondary mineral in the oxidised zone of some copper deposits, formed by alteration of arsenopyrite or enargite.