1911 Encyclopædia Britannica/Melaconite

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MELACONITE, a mineral consisting of cupric oxide, CuO, and known also as black copper ore. In appearance it is strikingly different from cuprite (q.v.) or red copper ore, which is cuprous oxide. Crystals are rare; they belong to the monoclinic, or possibly to the anorthic system, and have the form of thin triangular or hexagonal scales with a steel-grey colour and brilliant metallic lustre. More often the mineral is massive, earthy or pulverulent, and has a dull iron-black colour. Hence the name melaconite, from the Greek μέλας, black and κόνις, dust, which was originally given by F. S. Beudant in 1832 in the form melaconise. The crystallized Vesuvian mineral was later named tenorite, a name commonly adopted for the species. The hardness of the crystals is 3-4, but the earthy and powdery forms readily soil the fingers; the spec. grav. is 5.9. Crystals have been found only at Mt Vesuvius, where they encrust lava, and in Cornwall. The other forms of the mineral, however, are common in copper mines, and have resulted by the alteration of chalcocite, chalcopyrite and other copper ores, on which they often form a superficial coating.  (L. J. S.)