Malachite

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Malachite
Malachite specimen
General
Category	Carbonate mineral
Chemical formula	CuCO3.Cu(OH)2
Identification
Color	Bright green to blackish green
Crystal habit	Massive, botryoidal, stalactitic
Crystal system	Monoclinic - prismatic
Cleavage	Perfect on [201] fair on [010]
Fracture	Conchoidal to splintery
Mohs Scale hardness	3.5 - 4.0
Luster	Dull/vitreous in large quantities, silky in crystal form
Streak	light green
Diaphaneity	Transparent to translucent
Specific gravity	3.6 - 4
Optical properties	Biaxial (-)
Refractive index	nα = 1.655 nβ = 1.875 nγ = 1.909
Birefringence	δ = 0.254
References	[1][2]

Malachite is a carbonate mineral normally known as "copper carbonate" with the formula CuCO₃.Cu(OH)₂. This green-colored mineral crystallizes in the monoclinic crystal system, and most often forms botryoidal, fibrous, or stalagmitic masses. Individual crystals are rare but do occur as slender to acicular prisms. Pseudomorphs after more tabular or blocky azurite crystals also occur.

[edit] Etymology and history

The stone's name derives (via Latin and French) from Greek molochitis, "mallow-green stone", from molochē, variant of malachē, "mallow". 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 varying in color. The natural form was being replaced by its synthetic form, verditer amongst other synthetic greens. It is also used for decorative purposes, such as in the Malachite Room in the Hermitage, which features a large malachite vase (unknown scale). "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.

[edit] Occurrence and historical uses

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 its vibrant green color, the properties of malachite are similar to those of azurite and aggregates of the two minerals occur frequently together. Malachite is more common than azurite and is typically associated with copper deposits around limestones, the source of the carbonate.

Large quantities of malachite have been mined in the Urals. It is found in the Democratic Republic of Congo; Zambia; Tsumeb; Namibia; Russia; Mexico; Broken Hill, New South Wales; England; Lyon; and in the Southwestern United States especially in Arkansas and Arizona. In Israel, malachite is extensively mined at Timna valley, often called King Solomon's Mines although research has shown that the site was not in use during the 10th century.^[3]. Archeological evidence indicates that the mineral has been mined and smelted at the site for over 3,000 years. Most of Timna's current production is also smelted, but the finest pieces are worked into silver jewelry.

In Greek mythology, the throne of Demeter, goddess of grain and harvest, was fashioned from malachite and adorned with golden pigs and ears of barley.^[4]

[edit] Gallery

Malachite from the Democratic Republic of Congo	A polished slice of Malachite	Malachite	Malachite crystals atop blue azurite, with brown cuprite on the white kaolinite
Ball-and-stick model of malachite's unit cell	Polished Malachite	Malachite earrings and pendants in a shop window in England	Malachite from Browns Deposit, Rum Jungle, Northern Territory, Australia.jpg Malachite from Browns Deposit, Run Jungle, Northern Territory, Australia

[edit] References

• Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., John Wiley and Sons, New York ISBN 0-471-80580-7
• Mineral Galleries
• Virtual tour of the Malachite Room

[edit] See also

• aventurine
• dioptase

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