malachite

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For more information on malachite, visit Britannica.com.

A bright-green, basic carbonate of copper [Cu₂CO₃(OH)₂]. Malachite is the most stable copper mineral in natural environments in contact with the atmosphere and hydrosphere. It occurs as an ore mineral in oxidized copper sulfide deposits; as a stain on fractures in rock outcrops; as a corrosion product of copper and its alloys (except in industrial-urban environments, where the basic copper sulfate dominates); as suspended particles in streams and in alluvial sediments; and as encrustations on bronze artifacts in seawater and on cocco-liths floating in the oceans. It can be distinguished from other green copper minerals by its effervescence in acid. The combination of hardness (3.5–4 on Mohs scale) ideal for carving, color variation in concentric layers, and adamantine-to-silky luster has made malachite a highly prized ornamental stone. Its rare blocky-tabular crystals up to 5 mm (0.2 in.), its pseudomorphs after azurite crystals to 2 cm (0.8 in.), and its more common felty tufts perched on bright blue azurite are eagerly sought by mineral collectors. Malachite is an important copper ore mineral in supergene copper oxide deposits formed by weathering of primary copper sulfide deposits. See also Azurite; Carbonate minerals; Copper.

A carbonate of copper; green in color; harder than marble; usually employed as a highly polished veneer.

A precious stone (a variety of topaz) of basic copper carbonate. Folklore held that it preserved the cradle of an infant from spells.

Environment

Secondary (weathered) zone of copper ore deposits.

Usually in fibrous and silky crusts and masses; individualized single crystals are rare. When found they are usually silky-appearing twins with a re-entrant angle showing at the top. Also massive and earthy, often as thin films staining rock.

Light to dark green. Luster usually silky, crystals vitreous; hardness 3Ɖ-4; specific gravity 3.9-4.0; streak green; fracture usually splintery; cleavage basal, visible in the rare single crystals and sometimes across crusts. Brittle; opaque to translucent.

Copper carbonate (71.9% CuO, 19.9% CO ₂ , 8.2% H ₂ O).

Dissolves readily in hydrochloric acid with the release of bubbles. Gives all copper tests: solution color, bead test, copper bead on charcoal, and flame color.

Its intense green color shows it to be a copper mineral, but, in case of any doubt, a test could be made to make sure that it is not a chromium or nickel green. Likely to be confused with numerous copper sulfates, arsenates, and phosphates, but the effervescence as it dissolves in the hydrochloric acid eliminates them and proves it to be a carbonate.

The most common and most stable of the secondary ores of copper, always forming as a consequence of the weathering of primary copper sulfides. In its environment, it is so abundant that it constitutes an important ore, frequently appearing in the capping over a copper deposit, together with azurite, cuprite, and native copper.

Malachite usually forms fibrous crusts and masses. In a very compact form it was extensively used in Russia for carvings and mosaics. Since it varies considerably in hardness and may be poorly consolidated, only the hardest masses are suitable for this use. Several African countries still produce this dense lapidary material. Some years ago specimens were abundant at the famous Copper Queen Mine at Bisbee, Arizona, though most Arizona occurrences are soft, almost velvety crusts of slender needles, stalactites, and stalagmites, layered masses frequently alternating with bands of azurite, a constant associate.

Crystals of malachite are rare and usually small; few are over 1/16 in. (2 mm) across. The best have come from Germany, Russia, Namibia, Zaire, and sw. U.S. Large pseudomorphs composed of radiating velvety malachite needles, which seem to start from several centers on each surface, result from the alteration of dark blue crystals of azurite. Most recently the largest malachite crystals have come from the Ongonja Mine, Namibia, but previously they came from other localities, particularly Arizona and Morocco. A few large pseudomorphs after giant azurites like those of Tsumeb have been found in Michoacán, Mexico.

• Mineral compounds
• Gemstones
• Green

For other uses, see Malachite (disambiguation).

Malachite
Malachite from the Congo
General
Category	Carbonate mineral
Chemical formula	Cu2CO3(OH)2
Strunz classification	05.BA.10
Identification
Molar mass	221.1 g/mol
Color	Bright green, dark green, blackish green, commonly banded in masses; green to yellowish green in transmitted light
Crystal habit	Massive, botryoidal, stalactitic, crystals are acicular to tabular prismatic
Crystal system	Monoclinic—prismatic H-M Symbol (2/m) Space group P21/a
Twinning	Common as contact or penetration twins on {100} and {201}. Polysynthetic twinning also present.
Cleavage	Perfect on {201} fair on {010}
Fracture	Subconchoidal to uneven
Mohs scale hardness	3.5–4.0
Luster	Adamantine to vitreous; silky if fibrous; dull to earthy if massive
Streak	light green
Diaphaneity	Translucent to opaque
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][3]

Malachite is a copper carbonate hydroxide mineral, with the formula Cu₂CO₃(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.^[3]

Contents 1 Etymology and history 2 Occurrence 3 Malachite gallery 4 See also 5 References 6 Further reading

Etymology and history

The stone's name derives (via Latin: molochītis, Middle French: melochite, and Middle English melochites) from Greek Μολοχίτης λίθος molochitis lithos, "mallow-green stone", from μολόχη molōchē, variant of μαλάχη malāchē, "mallow".^[4] The mineral was given this name due to its resemblance to the leaves of the Mallow plant.^[5]

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. "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.

Archeological evidence indicates that the mineral has been mined and smelted at Timna valley in Israel for over 3,000 years.^[6]

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 its vibrant green color, the properties of malachite are similar to those of azurite and aggregates of the two minerals occur frequently. 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, Russia. It is found worldwide including in the Democratic Republic of Congo; Gabon; Zambia; Tsumeb, Namibia; Mexico; Broken Hill, New South Wales; Lyon, France; Timna valley, Israel, and in the Southwestern United States notably in Arizona.^[7]

Malachite gallery

• 

  Slice through a double stalactite, from Kolwezi, Democratic Republic of Congo. Size 5.9 × 3.9 × 0.7 cm.

• 

  A polished slab of malachite, from the Democratic Republic of Congo

• 

  Ball-and-stick model of malachite's unit cell

• 

  Malachite and azurite, from Morenci, Arizona USA. Size 4.4×4.1×2.2 cm.

• 

  Malachite stalactites (to 9 cm height), from Kasompi Mine, Katanga Province, Democratic Republic of Congo. Size: 21.6×16.0×11.9 cm.

• 

  Botryoidal malachite from Bisbee, Arizona USA. Size 10.5×6.3×5.6 cm.

• 

  Neoclassical vase in malachite in the Hermitage Museum, St Petersburg

See also

• Aventurine
• Azurite
• Brochantite
• Chrysocolla
• Dioptase
• Plancheite

References

1. ^ Malachite in Handbook of Mineralogy
2. ^ Malachite at Webmineral
3. ^ ^{a b} Malachite at Mindat
4. ^ Malachite, Dictionary.com
5. ^ Harper, Douglas. "malachite". Online Etymology Dictionary. http://www.etymonline.com/index.php?term=malachite. 
6. ^ Parr, Peter J review of "Timma: Valley of the Biblical Copper Mines" by Beno Rothenberg Bulletin of the School of Oriental and African Studies, University of London, Vol. 37, No. 1, In Memory of W. H. Whiteley (1974), pp. 223–224
7. ^ Mindat map with over 8500 locations

Further reading

Look up malachite in Wiktionary, the free dictionary.

Wikimedia Commons has media related to: Malachite

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

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