# Atacamite

- Page: https://taslar.bumba.tr/en/stones/atacamite/
- Turkish: Atakamit
- Kind: Mineral
- Classification: Minerals › Halides
- Chemical formula: Cu₂Cl(OH)₃
- Crystal system: Orthorhombic
- Hardness (Mohs): 3–3.5
- Specific gravity: 3.75–3.78 g/cm³
- Lustre: Adamantine, Vitreous (glassy)
- Transparency: Transparent, Translucent
- Colours: bright green, dark emerald green, blackish green
- Streak: Apple green
- Cleavage: Perfect on {010}; fair on {101}
- Fracture: Conchoidal; brittle
- Value ladder: 3/9 step, Building and industrial stone
- Last checked: 2026-10-04

The green copper mineral of deserts: named after the Atacama, it also forms on ancient bronzes corroding in the sea.

Atacamite is a dark green mineral made of copper, chlorine, oxygen and hydrogen (Cu₂Cl(OH)₃). It forms when copper minerals break down, especially under arid, saline conditions. It was described in 1802 from deposits in Chile's Atacama Desert and is named after it. In some deposits it is mined as a copper ore. It also forms on ancient bronze and copper objects left in the sea or the soil.

## How does it form?

Atacamite forms when other copper minerals break down on contact with air, most often under arid, saline conditions, that is, in deserts. It also forms at volcanic vents (fumaroles), from the weathering of sulfides at hot springs on the ocean floor (“black smokers”), and as ancient bronze and copper objects alter over time. Its crystals can reach 10 cm long. It has three relatives with the same composition but different crystal structures: paratacamite, clinoatacamite and botallackite.

## What is it used for?

- **Copper ore:** It is an ore mineral at the Chuquicamata mine in Chile.
- **Pigment:** Historically it was used as a green pigment in sculpture, manuscripts, maps and frescoes.
- **Archaeology:** Its formation on ancient bronzes helps explain how such objects decay.
- **Collecting:** Its dark green, lustrous crystals are sought by collectors.

## How to recognise it

- Bright green, dark emerald green or blackish green; its streak is apple green.
- Its crystals are slender prisms or tablets; it is usually fibrous, sandy-granular or massive.
- Adamantine to vitreous lustre.
- Hardness 3–3.5; a knife scratches it.
- Found with copper minerals such as cuprite, brochantite, malachite and chrysocolla.

## Fakes and imitations

- Malachite is also a green copper mineral, but it is usually banded and massive, and it fizzes in dilute acid (it is a carbonate). Atacamite does not fizz and often forms dark green, lustrous crystals.
- Paratacamite, clinoatacamite and botallackite have the same composition as atacamite but different crystal structures; telling them apart takes laboratory study.

## What determines its value?

Atacamite has value as a copper ore in some deposits, such as Chuquicamata in Chile. Collectors look for dark emerald-green, lustrous, sharp crystals and twinned groups; specimens from Chile and South Australia are well known.

This information is educational, not buying, selling or investment advice. Value varies enormously with quality and treatment.

## Myths and misconceptions

- Myth: Atacamite is found only in Chile's Atacama Desert. Fact: Although it is named after the Atacama Desert, atacamite occurs in small amounts in many copper deposits worldwide. It is also found in Mexico, the USA, Australia and on Italy's volcanoes, and can even form on ancient bronze objects.

## Curious questions

**What is the green crust on old bronze objects?**

Part of these crusts is atacamite. Copper and bronze objects break down, especially in contact with salt water or salty soil, and green copper chloride minerals form on their surface. The bronze of the famous Antikythera mechanism had turned to atacamite on the sea floor.

## Did you know?

- The bronze of the Antikythera mechanism had turned to atacamite during its centuries on the sea floor.
- Atacamite also occurs in the jaws of bloodworms, which make it themselves to harden their jaws.
- It has been found as a pigment in sculpture, manuscripts, maps and frescoes across Eurasia.

## Where is it found?

- Chuquicamata, Antofagasta, Chile (Major deposit): An ore mineral here, according to the Handbook of Mineralogy; in the Atacama Desert that gave the mineral its name
- Copiapó area, Atacama, Chile (Type locality): Atacamite was described in 1802 from deposits in the Atacama Desert; the exact original locality is unknown, and it is now known from many places around Copiapó
- Moonta, South Australia (Known locality): Yields large crystals, according to the Handbook of Mineralogy
- Bisbee, Arizona, USA (Known locality): A famous copper-mining town where atacamite also occurs
- Vesuvius, Campania, Italy (Known locality): An example of atacamite forming at volcanic vents (fumaroles)

## Sources

- [Atacamite](https://en.wikipedia.org/wiki/Atacamite), Wikipedia
- [Handbook of Mineralogy: Atacamite](https://www.handbookofmineralogy.org/pdfs/atacamite.pdf), Mineralogical Society of America
- [Chuquicamata](https://en.wikipedia.org/wiki/Chuquicamata), Wikipedia


Source: https://taslar.bumba.tr/en/stones/atacamite/ · Licence: CC BY-SA 4.0