Sulphides: Covellite

Diagnostic card.
Two samples of covellite - a mineral is rarely represented in a distinctly crystalline form.

Cu S (copper sulphide)
Shingoniya hexagonal
Hardness 1.5-2
Specific weight 4.59-4.76
Cleavage is perfect
Rough fracture
Color bluish-black, rainbow
Color in powder gray-blue
Glitter semimetallic

Cowelline (copper indigo), - copper sulfide. The gloss is metallic or greasy, opaque. The color and the trait are dark blue to blue-black. The fracture is uneven to shell. Cleavage is very perfect. Occurs in the zones of carburizing of copper deposits. Crystals (hexagonal syngony) are very rare, mainly dense masses, granular or powdery aggregates. A useful component of copper ores. Places of manifestation: Germany, Germany, Yugoslavia, USA, Chile, New Zealand.

Crystals are rather rare and always very thin, flattened in the form of a table with hexagonal outlines. Hatching is often observed on the most developed face surfaces. You can meet isolated individuals, as well as fused as rosettes or grouped in the form of subparallel plates.

Chemical composition. Copper (Cu) 66.5%, sulfur (S) 33.5%. Form of crystalline precipitates. Most often, small thin plates, leafy, fine-grained, piecemeal, solid masses. Crystal structure. Hexagonal layered lattice. Class of symmetry. Dihexagonally bipyramidal - 6 / mmm. Cleavage. Perfect in the basis of (0001). Aggregates. Massive, solid, leafy.

Diagnostic signs.
Cowellin is a characteristic and very catchy mineral. It is difficult to confuse with others due to its spectacular bluish-black color and bright semimetallic luster. He is very soft, scratching his fingernail, but quite heavy. In addition, its thinnest plates are flexible, they easily bend, not breaking. Easily melts and lights up with a blue flame, emitting sulfur dioxide.

Origin.
Cowellin is a mineral of essentially secondary origin. It is formed in the oxidation zones of sulfide copper deposits, where it is mainly associated with chalcopyrite, bornite, pyrite and (mainly) enargite. Much rarer it is the result of sublimation (direct deposition upon cooling from the vapor state) in Vesuvius fumaroles. There it is found in the form of crusts of azure blue.

Deposits and applications.
Cowellin is found in various parts of Italy. The rarest finds of crystals up to 1 cm in diameter are made in marbles of Carrara. Several good specimens were found at the Bor deposit in eastern Serbia; Beautiful crystals are found in different places in America (USA), especially in Butte, Montana, and in Kennekot, Alaska. There it is represented in significant quantities and extracted for copper recovery.

Cowellin. Alghero, near Sassari, Sardinia, Italy (EC). Photo: © А.А. Evseev.

Cowelline is crystalline in pyrite. Bor mine, Serbia (EC). Photo: © А.А. Evseev.

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