A cheaper alternative to Lapis Lazuli was the mineral Azurite (basic copper carbonate) found in deposits of copper ore.
Used since antiquity, Azurite is is the sister-stone to malachite, to which it is chemically related. Preparation of mineral azurite as a pigment was to simply grind, wash and sieve. When very nely ground, azurite is a pale sky-blue with a hint of green, excellent for skies, but inferior to the purple richness of ultramarine. If ground more coarsely, a deeper tone is achieved, but is very gritty, making the paint more translucent and dif cult to apply so that many coats of coarse Azurite needed to be applied to achieve an opaque colour.
Both azurite and azure are derived via Arabic from the Persian word lazhward (دروژال). In Europe it was known as lapis armenius, German azure or Mountain Blue.
Confusion between azurite and lapis lazuli was common. Although the two are chemically quite different, they have a very similar appearance. To tell them apart, the careful apothecarist would heat a sample of the mineral until they were red-hot: azurite turns black on cooling, lapis lazuli does not.
Azurite was the most important blue pigment in European painting throughout the middle ages and Renaissance.
It fell out of use when Prussian blue was discovered in the early 18th century.