carbonates
Azurite
Cu3(CO3)2(OH)2
- Also known as
- chessyliteazurmalachite
- Crystal system
- monoclinic
- Hardness
- 3.5–4 on the Mohs scale
- Lustre
- vitreous
- Colour
- Deep azure to violet blue
- Where it forms
- With malachite in the oxidised zone of copper deposits, and less stable than it: azurite slowly converts to malachite in the presence of water, which is why many specimens are part-converted.
- Chiefly from
- MoroccoArizona, United StatesNamibiaAustralia
Why it is that colour
Copper again — the same element that makes malachite green. The difference is the ratio of carbonate to hydroxide, and that small difference in structure changes how the copper absorbs light.
Safety
As malachite. A soft copper carbonate, soluble in acid, and not to be put in water, in a mouth, or into dust.
Where it comes from
Moroccan and Namibian specimen material dominates. Volumes are small; azurite is not a bulk trade stone.
Historical use
The principal blue pigment of European painting before ultramarine became affordable — cheaper than lapis and used underneath it, or instead of it, in a great many paintings. Its conversion to malachite over centuries is why some medieval skies are now green, and conservators can sometimes demonstrate that a green robe was painted blue.
Recorded as history and attributed where possible. That a stone was used for something establishes that people used it, not that it worked.
What is attributed to it, and since when
Used as a pigment throughout the medieval and Renaissance world, and treated in European lapidaries as a stone of the heavens because of its colour. Its modern association with insight and intuition follows the same colour logic and is recent.
Described, not endorsed. Dating a claim is not the same as assessing it — but an association that first appears in a book published in 1985 is not an ancient inheritance, whatever the label says. A sincere account of feeling better is compatible with the stone doing nothing — see the placebo effect.
Sold as this, but not
Worth knowing
The green skies of certain medieval paintings are a genuine and slightly melancholy piece of chemistry. Azurite is metastable: given moisture and time it turns into malachite, which is green. Paintings that left the workshop with blue heavens have quietly become green, and the artist's intention has to be reconstructed from what the pigment used to be.
It is also a reminder that "natural" and "stable" are unrelated ideas. This is a natural mineral which decomposes into a different natural mineral if you leave it somewhere damp.
Identity checked against IMA-CNMNC master list, June 2025.