1911 Encyclopædia Britannica/Azurite
AZURITE, or Chessylite, a mineral which is a basic copper carbonate, 2CuCO3·Cu(OH)2. In its vivid blue colour it contrasts strikingly with the emerald-green malachite, also a basic copper carbonate, but containing rather more water and less carbon dioxide. It was known to Pliny under the name caeruleum, and the modern name azurite (given by F. S. Beudant in 1824) also has reference to the azure-blue colour; the name chessylite, also in common use, is of later date (1852), and is from the locality, Chessy near Lyons, which has supplied the best crystallized specimens of the mineral. Crystals of azurite belong to the monoclinic system; they have a vitreous lustre and are translucent. The streak is blue, but lighter than the colour of the mineral in mass. Hardness 3½–4; sp. gr. 3.8.
Azurite occurs with malachite in the upper portions of deposits of copper ore, and owes its origin to the alteration of the sulphide or of native copper by water containing carbon dioxide and oxygen. It is thus a common mineral in all copper mines, and sometimes occurs in large masses, as in Arizona and in South Australia, where it has been worked as an ore of copper, of which element it contains 55%. Being less hydrated than malachite it is itself liable to alteration into this mineral, and pseudomorphs of malachite after azurite are not uncommon. Occasionally the massive material is cut and polished for decorative purposes, though the application in this direction is far less extensive than that of malachite. (L. J. S.)