Usually occurs in nodular or incrusting masses; hardness 3.5; specific gravity 4; color green; streak a lighter green; luster adamantine, silky or dull; translucent on thin edges.
The vivid green of malachite is usually enough to determine it at once, but one may be sure by trying a drop of acid on it, in which case it effervesces as is characteristic of so many carbonates, but this is the only carbonate which is vivid green. Generally the malachite is in irregular masses, but crystals are occasionally found. These are extremely small and needle-like, and belong to the monoclinic system. In the Ural Mountains there is a locality where these crystals grow in fibrous masses, usually radiating from the center. Malachite in such nodules has a silky luster. These rare nodules have furnished the rulers of Russia with a unique and much prized material for making royal gifts. In European museums and palaces one finds many objects carved from this form of malachite, and marked as gifts of the czars of Russia.
In the United States malachite is widely distributed, appearing as green streaks and stains where copper minerals have been exposed to the air. It is the green tarnish which appears on bronze and copper when exposed to the weather. It is found in large quantities in New Jersey, Pennsylvania, Wisconsin, Nevada, Arizona, Utah, New Mexico, etc. The Bisbee mine in Arizona is the place that has furnished museums with so many of the handsome specimens of malachite associated with azurite. These are the most striking specimens for the vividness of their colors that appear in any collections.
Malachite has been known since about 4000 B.C., the Egyptians having mines where they obtained it between the Suez and Mt. Sinai. In those early days it was particularly a child’s charm, protecting the wearer from evil spirits. It is still used as a stone of lesser value in making some sorts of jewelry.
[Azurite]
2CuCO₃·Cu(OH)₂
[Pl. 11]
Occurs as short prismatic or tabular crystals of the monoclinic system; hardness 4; specific gravity 3.8; color azure blue; streak lighter blue; luster vitreous; translucent on thin edges.
Azurite is another very striking mineral fully characterized by its color and streak. Like malachite it effervesces in acid. It is very near to malachite in composition, and by increasing its water content, can and freely does change to the green mineral; so that few specimens of azurite are without traces of malachite. It is found in the same places as malachite, but is not as abundant in the east.
Azurite with the accompanying malachite is cut and polished to make semi-precious stones for some forms of jewelry.
[Chrysocolla]
CuSiO₃·2H₂O
Never occurs in crystals, but in seams and incrustations; hardness 2-4; specific gravity 2.1; color bluish-green; streak white; luster vitreous; translucent on thin edges.