Azurite
A deep-blue copper mineral used as pigment since antiquity.
Azurite, also known as Azure spar or chessylite, is a soft, deep-blue copper mineral produced by weathering of copper ore deposits. It has been known since ancient times and was mentioned in Pliny the Elder's Natural History under the Greek name kuanos and the Latin name caeruleum. The mineral, a basic carbonate with the formula Cu3(CO3)2(OH)2, has been used as a blue pigment since antiquity and is a popular collector's stone.
- formula
- Cu3(CO3)2(OH)2
- hardness
- 3.5 to 4 (Mohs)
- specific_gravity
- 3.7 to 3.9
- crystal_system
- Monoclinic
- color
- Deep blue
- type_locality
- Chessy near Lyon, France
Lore & Background
Azurite crystallizes in the monoclinic system, with large crystals often prismatic and dark blue. Specimens can be massive, nodular, or occur as drusy crystals lining a cavity. The mineral effervesces upon treatment with hydrochloric acid, a characteristic of carbonates. Its deep blue color results from copper(II) ions and low energy d-d transitions. Azurite is unstable in open air compared to malachite and often pseudomorphically replaced by malachite, a process involving replacement of water with carbon dioxide. Under ordinary storage conditions, azurite is quite stable and retains its color for long periods.
Reader's Guide
Azurite has been used as a blue pigment since ancient times, with examples found in Egyptian Fourth Dynasty pallets, Fifth Dynasty mummy cloth, and Eighteenth Dynasty wall paintings. It was known as mountain blue, Armenian stone, and azurro della Magna. When mixed with oil it turns slightly green; with egg yolk it turns green-grey. Heating distinguishes azurite from ultramarine: azurite converts to black copper oxide, while ultramarine withstands heat. Azurite is used occasionally as beads and jewelry, though its softness and tendency to weather limit its use. It is a popular collector's stone, and the notion that specimens must be carefully protected from bright light, heat, and open air may be an urban legend. Azurite is a good surface indicator of weathered copper sulfide ores, usually found with malachite.
Did You Know?
- Azurite was mentioned in Pliny the Elder's Natural History under the Greek name kuanos, root of the English word cyan.
- Azurite is one of two relatively common basic copper(II) carbonate minerals, the other being malachite.
- The best azurite crystals, up to 10 inches in length, are found at Tsumeb, Namibia.
- Gentle heating of azurite produces a deep blue pigment used in Japanese painting techniques.
Frequently Asked Questions
What is Azurite?
Azurite is a soft, deep-blue copper mineral that forms as copper ore deposits undergo weathering. It goes by the alternate names Azure spar and chessylite, and has been recognized by humans since ancient times.
What is Azurite's chemical formula and crystal system?
Its formula is Cu3(CO3)2(OH)2, classifying it as a basic copper carbonate. It crystallizes in the monoclinic system and has a specific gravity ranging from 3.7 to 3.9.
How hard is Azurite on the Mohs scale?
Azurite rates between 3.5 and 4 on the Mohs hardness scale, making it soft enough to be scratched by a steel nail. This relative softness makes it easy to polish into cabochons but also means collectors must handle specimens with care.
Why is Azurite historically significant as a pigment?
It has been ground into a blue pigment since antiquity, and Pliny the Elder referenced it in his Natural History under the Greek name kuanos and the Latin caeruleum. Its intense, deep blue made it one of the most valued natural pigments before synthetic dyes became available.
Where is Azurite's type locality?
The type locality is the town of Chessy, near Lyon, France, where the mineral was first formally described. This origin is the source of its alternate name, chessylite.
More in Minerals & Crystals 1-24
Elsewhere in the Minerals & Crystals universe
Spotted an error? Know more?
This is a living reference — every entry is fact-audited, and reader corrections feed straight into our audit queue. Suggest an edit · See this site's audit record