Formula: Cu₁₈Al₂(AsO₄)₄(SO₄)₃(OH)₂₄ · 36H₂O

Species:

Colour: Emerald green, grass green, bluish green, blue; green in transmitted light

Lustre: Sub-Adamantine, Vitreous, Pearly

Hardness: 2

Specific Gravity: 2.67 – 2.69

Crystal System: Trigonal. An uncommon secondary mineral occurring in the oxidized zones of some arsenic-bearing hydrothermal polymetallic deposits. Can be partially dehydrated.

Name: From the Greek χαλκός (chalkos) for “copper” and φύλλον (phullon) for “leaf,” in allusion to the composition, containing copper, and the platy habit of the crystals.

Type Locality: Cornwall – England, UK