Malachite
A green copper carbonate — an ore, the oldest green pigment, and a banded ornamental stone, all from the same weathered copper deposit.
Malachite is what copper turns into near the surface. Where a copper deposit is exposed to air and carbonated groundwater, the primary sulfides break down and re-form as carbonates, and malachite is the commonest of them — which is why a green stain on rock has been a prospecting sign for as long as people have looked for copper.
It has been three things at once for most of that history: an ore easy enough to smelt that it plausibly carried the beginning of metalworking, a pigment, and a stone worth cutting for its concentric green banding.
How to identify it
The green is diagnostic and so is the streak, which is pale green rather than white. Massive malachite shows concentric bands of light and dark green from successive deposition, and it fizzes in dilute acid like any carbonate.
It is soft — around 3.5 to 4 — which is why polished malachite scratches easily and why it is used for ornament rather than for anything that will be handled hard.
Cultural significance
Ground malachite was one of the earliest green pigments and appears in Egyptian painting and cosmetics, and later throughout medieval European work. It is not lightfast in oil and darkens, which is part of why so much old green now reads as brown or black.
As an ornamental stone it was worked at scale in Russia in the nineteenth century, veneered onto columns, tables and whole rooms in a way that made a soft mineral behave like architecture.
How we know: checked recently · only one source, so there is nothing to cross-check it against · stated directly by the source.
How this connects
Where a connection has been confirmed by an outside reference, that reference is named beside it.
is an ore of
- Copper — element · a secondary ore, formed where a copper deposit has weathered Wikidata
is an alternative to
- Chalcopyrite — mineral · as copper ore, and the choice decides the plant rather than the feed: chalcopyrite is a sulfide and goes to flotation and a smelter, malachite is a carbonate that dissolves in acid and goes to leaching and electrowinning. Most porphyry deposits have both, the oxidised one on top
- Azurite — mineral · the two oxidised copper carbonates, mined together and treated identically. Azurite is the less stable of the pair and slowly alters to malachite, which is why green outcrops are commoner than blue ones
is a component of
- Oxidised zone — deposit type · the green copper carbonate, and the mineral pre-industrial copper was almost entirely smelted from — no roasting needed
is an input to
- Solvent extraction and electrowinning — process · a carbonate dissolves straight into acid, which is why an oxidised orebody goes to a leach pad and the sulfide beneath it goes to a smelter
Sources
- Material WorldOur own writing
- Wikimedia Foundation · Creative Commons CC0 1.0 Universal (public domain dedication)
- COD Advisory Board / Vilnius University · CC0 — contributors place data in the public domain