Malachite

Malachite
Malachite Macro 43.jpg
Malachite showing typical radiating fibrous and botryoidal structure.
General
Category Mineral
Chemical formula Cu2CO3(OH)2
Identification
Color Green
Crystal habit Massive, botryoidal, stalactitic
Crystal system Monoclinic - prismatic
Cleavage Perfect
Fracture Conchoidal to splintery
Mohs Scale hardness 3.5 - 4
Luster Dull/vitreous in large quantities, silky in crystal form
Streak green
Specific gravity 3.6 - 4

Malachite is a carbonate mineral of copper, with a vibrant green color. It is usually found with copper deposits associated with limestone. It has been used to make decorative objects and as a pigment in green paints for thousands of years.

Contents

Etymology

The name malachite derives (via Latin and French) from the Greek word molochitis, meaning "mallow-green stone." That, in turn, may be derived from molochē (variant of malachē), meaning "mallow."

Occurrence

Malachite often results from weathering of copper ores and is often found together with azurite (Cu3(CO3)2(OH)2), goethite, and calcite. Except for the vibrant green color, the properties of malachite are very similar to those of azurite and aggregates of the two minerals together are frequently found, although malachite is more common than azurite. Typically found with copper deposits associated with limestone, the source of the carbonate.

Large quantities of malachite have been mined in the Ural mountains of Russia. In addition, it has been found in the Democratic Republic of Congo; Tsumeb, Namibia; Mexico; Broken Hill, New South Wales, Australia; England; and Lyon, France. It also occurs in the Southwestern United States, especially in Arizona at Bisbee and Morenci.

In Israel, malachite is extensively mined at Timna, often called King Solomon's Mines. Archeological evidence indicates that the mineral has been mined and smelted at this site for over 3,000 years. Most of Timna's current production is also smelted, but the finest pieces are worked into silver jewelry.

Characteristics

Ball-and-stick model of a unit cell malachite.

Chemically, malachite is called copper(II) carbonate hydroxide, with the formula Cu2CO3(OH)2. It crystallizes in the monoclinic crystal system, and most often forms botryoidal, fibrous, or stalagmitic masses. Individual crystals are rare, but they do occur as slender to acicular prisms. Pseudomorphs after more tabular or blocky azurite crystals also occur.

Uses

Malachite was used as a mineral pigment in green paints from antiquity until about 1800. The pigment is moderately lightfast, very sensitive to acids, and varies in color. The natural form was being replaced by its synthetic form, verditer, amongst other synthetic greens.

It is also used for decorative purposes. For instance, the Malachite Room at the Hermitage Museum in St. Petersburg, Russia, features a huge malachite vase. "The Tazza," one of the largest pieces of malachite in North America and a gift from Tsar Nicholas II, stands as the focal point in the center of the room of Linda Hall Library in Kansas City, Missouri.

Gallery

See also

References

  • Hurlbut, Cornelius S., and Cornelis Klein. 1985. Manual of Mineralogy. 20th ed. New York: John Wiley. ISBN 0-471-80580-7
  • Sofianides, Anna S., and George E. Harlow. 1997. Gems & Crystals. London: Parkgate Books. ISBN 1-85585-391-4
  • Weinstein, Michael. 1967. The World of Jewel Stones. New York: Sheridan House.

External links

All links retrieved August 8, 2018.

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