What is Olivenite?
Olivenite is an olive-green copper arsenate celebrated for sharp crystals from oxidised copper deposits, especially the classic Tsumeb and Cornwall localities.
Mineralogy and crystal structure
Reference formula: Cu2AsO4OH. Olivenite belongs to the adelite-descloizite group. Its colour and chemistry grade toward related arsenates, so reliable locality and analysis are more useful than appearance alone. Olivenite is classified with phosphates and has a orthorhombic crystal system. Typical hardness is 3–3.5 on the Mohs scale and specific gravity is approximately 4.2–4.4.
Colour, lustre and habit
Typical colours include olive-green, yellow-green, brown, black. The usual prismatic, acicular, radiating habit and vitreous, resinous lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Olivenite forms in or is associated with oxidised zones of hydrothermal copper deposits and arsenic-rich cavities. Important documented localities include Tsumeb in Namibia, Cornwall in England, Chile, Mexico, France and the United States.
Olive-green crystals from the copper cap
Olivenite turns the weathering zone of a copper vein into a collector classic: slender orthorhombic crystals combine vivid colour with a story of arsenic-rich oxidation.
Collecting and care
Keep dry and enclosed; avoid dust, acids and any tasting or abrasive testing because arsenic minerals require sensible handling.
