Malachite

 

Malachite (Cu2CO3(OH)2) is a carbonate, which are among the most widely distributed minerals in the Earth's crust. Carbonate minerals other than simple carbonates include hydrated carbonates, bicarbonates, and compound carbonates. Malachite is a member of this third group, as are the minerals, bastnäsite, doverite, and azurite.

Malachite is a secondary mineral of copper, which means it is formed when copper minerals are altered by other chemicals. It occurs when carbonated water interacts with copper minerals, or when a solution of copper interacts with limestone. Malachite is opaque and always green. Because of its presence in nearly all oxidized copper deposits, malachite serves as a prospecting guide for copper.

Malachite crystals sometimes form as needles that fan out from the rock in which they are embedded. More often, malachite forms as a mass with concentric bands of light and dark green. Such specimens are almost always internally banded in different shades of green, and can be seen when a specimen is polished or cut open. When, the bands consist of concentric rings, specimens are highly prized.

Because of its beauty and relative softness, polished, banded Malachite has been carved into ornaments and worn as jewelry for thousands of years. In some cultures it was thought to be a protection from evil if worn as jewelry. Malachite has also been widely used as an ornamental stone. In Czarist Russia it was used to make the columns of St. Isaac's Cathedral in Leningrad. The original material, from which ornaments and jewelry were made since the earliest times came from an enormous deposit in the Ural Mountains of Russia, where massive globular specimens were found.

Malachite is still very popular among mineral collectors, especially interestingly shaped and banded specimens. It is also used as an ore of copper and crushed to make a green pigment. Malachite is usually found with azurite, a blue secondary mineral of copper, but its more widespread and abundant. Some mineral samples have alternating bands of green malachite and blue azurite, forming what is commonly known in the gem and mineral trade as Azure-malachite.

Malachite is found in Russia, Zaire, Australia, and Namibia, Zaire, South Africa, Australia, Germany, Romania, Chile, Mexico and the U.S. In the U.S., localities include Juab County Utah; Morenci, Greenlee, Globe, Gila, Ajo and Pima counties, Arizona; and Grant and Socorro counties in New Mexico. In the Copper Queen Mine of Bisbee, Arizona, large azurite crystals are found pseudomorphed by Malachite.

MALACHITE

Chemistry
Crystal System
Hardness
Cu2CO3(OH)2
Monoclinic
3.5 to 4 (Mohs' scale)
Cleavage
 Fracture
Specific Gravity
Perfect in one direction, crosswise
Conchoidal
splintery, brittle, scaly
3.7 to 3.9
VARIETIES
  Color, Transparency,
Luster & Streak
Cryolite
- Color:
Light green,
black green
- Transparency:
Transparent to opaque
- Luster:
Vitreous, silky, dull
- Streak:
Light green

-- Bob Katz


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