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Malachite Mineral Facts:

Chemical Formula: Cu₂CO₃(OH)₂  The Mineral is 54.7% Copper by weight.

Colors: Pure malachite is bright green in color and has a light green streak.

Hardness: 3.5 to 4

Density: 3.9

Cleavage: The basal cleavage is perfect parallel to P(001).

Crystallography: Monoclinic
Malachite usually occurs in fibrous, radiate, stalactitic, granular or earthy, green masses, or as small drusy crystals covering other copper compounds.  Well defined crystals are usually very small monoclinic prisms. Contact twins are common.

Luster:. Its luster is vitreous, but can be silky on surfaces broken parallel with the fibrous structure. Sometimes earthy or dull in massive forms.

Optics: (Refractive Index):  b = 1.88;

Fibrous Malachite

Composition, Structure and Associated Minerals:
Malachite is a frequent decomposition product of other copper minerals, being formed rapidly in moist places through the combination of copper and carbon dioxide from the air or dissolved from limestones. It occurs abundantly in the upper oxidized portions of veins and other deposits of copper ore, where it is associated with azurite, cuprite, native copper, limonite and the various sulfides of iron and copper. Commonly forms massive, encrusting, stalactitic, or stalagmitic growths having a smooth, mammillated or botryoidal surface with a fibrous and compact internal structure. It also commonly forms pseudomorphs after the crystal form of other copper minerals.

Malachite is an important and widely distributed copper ore of secondary origin. Commonly occurs in copper veins that lie in or near limestones. The color banding marks the successive deposits of the mineral, which has, in most cases, resulted from the percolation of water through copper-bearing rocks, and the subsequent deposition of the dissolved carbonate in fissures or cavities, the solution having apparently dripped in slowly, and the water evaporated, thus forming a series of layers in the same way that stalactites and stalagmites of calcite are formed by percolation of water through limestone.

The green stains and patina which are noticed on exposed copper trimmings of buildings, roofs or statues like the Statue of Liberty, is composed in a large part of this substance. The name is derived from the Greek word for mallows, in allusion to its green color.

Botryoidal Malachite

Identification and Diagnostics
Malachite, on account of its characteristic bright green color and radiating fibrous structure is easily recognized. It is soluble in hydrochloric acid with effervescence of carbon dioxide. The solution turns deep blue with excess of ammonia added (a test for the presence of copper). It  may be easily distinguished from all other minerals with the exception of some varieties of turquoise and a few other copper compounds, such as atacamite. Malachite may be distinguished from all of these other similar colored copper minerals by its effervescence with acids.

Uses:
Malachite is mined with other copper compounds at many mines, and it is an important ore of the metal. It is not separated from them in the mining or smelting process.

Polished Malachite

Occurrence, Localities and Origins:
Malachite is found in nearly all copper mines, where it occurs in the zone of weathering. As with most secondary minerals, water transports the copper down and concentrates it just above the water table. Large concentrations are often found below the surface gossan in rich copper lodes.

Notable localities for its occurrence in the United States it has been found in good specimens at Cornwall, Lebanon Co. Pennsylvania; at Mineral Point, Wisconsin; at the Copper Queen Mine, Bisbee, and at the Humming Bird Mine, Morenci, and other localities in Arizona. It is also important in the Tintic district, Utah, Nevada and in New Mexico. It is an an important copper ore in the all the major southwestern copper districts. 

Very large masses of banded, compact malachite which are suitable for many types of  decorative and architectural use have been procured from mines in Africa, Siberia and Australia.

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