Chemically, this material is a basic cupric carbonate with about 8 per cent of water. Heating will thus drive off the water with a resultant change in color, and to preserve the original shade, acids or liquids of any kind should not be brought into contact with it. Hydrochloric acid will attack malachite, and the effervescence caused by the chemical action would serve as a distinguishing test. Actually, the color alone is almost sufficient to distinguish malachite from any other stone or material. The green may be dark or light, but surfaces have a peculiarly porous or powdery look, even if the usual layers or rings of darker shades, generally concentrically formed, are not present. The green is quite often finely figured, the veins running in lines or in circles and ovals. A good polish may be obtained, and easy working on the lathe is facilitated by perfect cleavage. This stone is relatively heavy, the specific gravity being 3.9 to 4. Refraction is double, the readings generally obtained being approximately 1.88. The rough stone is found in masses over a wide area, but it also occurs very occasionally in crystal form, these being of the monoclinic system. Malachite is found associated with other copper ores, but large pieces suitable for working are rare.Nevertheless, prices are low, for the lack of hardness is a great drawback to its use in ornament. Carving, often of Chinese origin, inlay work of all kinds, and larger decorative work are the chief uses to which malachite has been put, and old pieces of jewelry containing this stone show that its easy working was acknowledged by early craftsmen. Nodular concretions of malachite are sometimes seen on ancient bronze implements which have been unearthed after many years of burial. The green stains seen on ore from all copper mines are due to malachite, this having been formed by the action of weathering agents on the other copper bearing minerals of the ore. The green patina on bronze is also due to the surface alteration to malachite, since bronze is about 80 per cent copper. The -Belgian Congo, Rhodesia, the U.S.S.R. and Australia produce most of the rough material used, but many mines which were once prolific are now exhausted, and the first two areas mentioned are now the chief sources of supply. Worked pieces are common in Russia, since the stone was mined in quantity in the Urals. Clock cases, vases, and even tables, chairs, and pillars are inlaid with this material, and some fine specimens may be seen in many churches and public buildings, particularly in the palaces and churches of Leningrad. St. Sophia, well known to visitors of Istanbul, is richly ornamented with malachite. Confusion with other stones is rare since malachite possesses characteristic properties, many of which are almost obvious superficially. Color, relative weight, and low hardness are properties which are quickly recognized, and perhaps chrysocolla is the only stone which approaches it in appearance. This latter often looks more blue than green and is more like poor turquoise matrix. The texture is harder, although it is also very soft. The term malachite is derived from a Greek word meaning "marshmallow," as it resembles the color of the leaves of this plant. |
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This opaque stone, distinguished by its green color, has been used in jewelry and larger decorative works for many centuries. On account of its lack of hardness and its consequent liability to fracture and lose its polish easily, it is not at all suitable to be used where it may be subjected to friction. It will be noticed that all jewelry containing malachite shows a deterioration on the surface polish of the stones, while if several pieces in the form of inlay have been used, some are invariably cracked or damaged. The polish can, however, be fairly easily restored since the hardness is only about 3 1/2 to 4 on Mohs' scale.