Malachite

Malachite
Malachite from the Congo
General
Category	Carbonate mineral
Formula (repeating unit)	Cu2CO3(OH)2
Strunz classification	05.BA.10
Identification
Formula 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 opaque, green banded mineral crystallizes in the monoclinic crystal system, and most often forms botryoidal, fibrous, or stalagmitic masses, in fractures and spaces, deep underground, where the water table and hydrothermal fluids provide the means for chemical precipitation. Individual crystals are rare but do occur as slender to acicular prisms. Pseudomorphs after more tabular or blocky azurite crystals also occur.^[3] Typical malachite is laminated and whether or not microbes intervene in its formation is unknown.

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 among other synthetic greens. It is also used for decorative purposes, such as in the Malachite Room in the Hermitage, which features a huge malachite vase and the Malachite Room in Castillo de Chapultepec in Mexico City. "The Tazza", a large malachite vase, 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] Since then, malachite has been used as both an ornamental stone and as a gemstone.

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 the Southwestern United States, most notably in Arizona.^[7]

Malachite gallery

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  Slice through a double stalactite, from Kolwezi, Democratic Republic of Congo. Size 5.9 × 3.9 × 0.7 cm.
  
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  A polished slab of malachite, from the Democratic Republic of Congo
  
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  Ball-and-stick model of malachite's unit cell
  
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  Malachite and azurite, from Morenci, Arizona USA. Size 4.4×4.1×2.2 cm.
  
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  Malachite stalactites (to 9 cm height), from Kasompi Mine, Katanga Province, Democratic Republic of Congo. Size: 21.6×16.0×11.9 cm.
  
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  Botryoidal malachite from Bisbee, Arizona USA. Size 10.5×6.3×5.6 cm.
  
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  Neoclassical vase in malachite in the Hermitage Museum, St Petersburg
  
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  Gothic-Style Bracelet with Malachite (circa 1870). The Walters Art Museum.
  

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.
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