What is Clinoclase

Clinoclase is a rare and visually striking secondary copper arsenate mineral with the chemical formula Cu₃(AsO₄)(OH)₃. It forms in the oxidized zones of copper deposits where arsenic is present, typically appearing as deep azure-blue to emerald-green acicular or prismatic crystals.

Associated minerals include malachite, olivenite, quartz, limonite, adamite, azurite, and brochantite among others.

Clinoclase was discovered in 1830 in the county of Cornwall in England. Abichite is another name for clinoclase. The mineral belongs to the monoclinic crystal system and exhibits perfect cleavage in one direction, a property reflected in its name—derived from the Greek klino (inclined) and klasis (breaking).

Clinoclase Crystals. Tin stope, Majuba Hill Mine, Antelope District, Pershing Co., Nevada, USA Photo Copyright © Elmar Lackner

Clinoclase Properties

• Color: Deep azure-blue, emerald-green, or bluish-black.
• Luster: Vitreous to subadamantine (approaching diamond-like luster in some cases).
• Streak: Pale blue to greenish.
• Hardness: 2.5–3 on the Mohs scale (relatively soft).
• Cleavage: Perfect in one direction (basal cleavage).
• Fracture: Uneven to subconchoidal.
• Density: 4.1–4.3 g/cm³ (relatively heavy for a non-metallic mineral).
• Clinoclase : Cu₃(AsO₄)(OH)₃
• Crystal System: Monoclinic
• Crystal System: Clinoclase crystallizes in the monoclinic crystal system.
• Habit: It typically occurs as acicular (needle-like) or prismatic crystals, but can also be found in radiating aggregates, crusts, or massive forms.
• Tenacity: brittle
• Occurrence: A rare secondary mineral in the oxidized zone of some arsenic-rich hydrothermal
• base-metal deposits.
• Association: Olivenite, cornwallite, cornubite, conichalcite.
• The type locality for clinoclase is the Wheal Gorland mine at St Day, Cornwall in the United Kingdom.