MALACHITE, a copper-ore of fine green colour, sometimes polished as an ornamental stone. The name is derived from Gr. [Greek: maláchê], the mallow, in allusion to the colour of the mineral being rather like that of the mallow-leaf. Malachite was perhaps one of the green minerals described by Theophrastus under the general name of [Greek: smaragdos]; and according to the late Rev. C. W. King it was probably the _smaragdus medicus_ of Pliny, whilst his _molochites_ seems to have been a different stone from our malachite and may have been a green jasper. It is suggested by J. L. Myres (_Ency. Bib._) that malachite may have been the Heb. _soham_, of the high priest's breastplate. Malachite is a basic cupric carbonate, represented by the formula CuCO3Cu(HO)2, and has usually been formed by the action of meteoric agencies on other copper-minerals; hence it is found in the upper part of ore-deposits, often as an incrustation, and occasionally as a pseudomorph after cuprite, chalcocite, &c. When formed, as commonly happens, by the alteration of copper-pyrites the iron of this mineral usually takes the form of limonite, which may remain associated with the malachite. Occasionally, though but rarely, malachite occurs in small dark-green prismatic crystals of the monoclinic system. Its usual mode of occurrence is in nodular or stalagmitic forms, with a mammillated, reniform or botryoidal surface, whilst in other cases it forms fibrous, compact or even earthy masses. The nodules, though commonly dull on the outside, may display on fracture a beautiful zonary structure, the successive layers often succeeding each other as curved deposits of light and dark tints. The colours include various shades of apple-green, grass-green, emerald-green and verdigris-green. Certain varieties exhibit a finely fibrous structure, producing on the fractured surface a soft silky sheen.