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 mono-clinic, 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 µEras, black and rthvis, 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. gray. 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 .