Malachite

For other uses, see Malachite (disambiguation).
Malachite

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]

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]

Archeological evidence indicates that the mineral has been mined and smelted to obtain copper 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.

Use

Malachite was used as a mineral pigment in green paints from antiquity until about 1800.[7] 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.

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. Ural malachite is not being mined at present,[8] but G.N Vertushkova reports the possible discovery of new deposits of malachite in the Urals.[9] It is found worldwide including in the Democratic Republic of the 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.[10]

Malachite gallery

See also

References

  1. ↑ Malachite in Handbook of Mineralogy
  2. ↑ Malachite at Webmineral
  3. 1 2 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. ↑ R.J. Gettens and E. W. Fitzhugh, Malachite and Green Verditer, in Artists’ Pigments. A Handbook of Their History and Characteristics, Vol. 2: A. Roy (Ed.) Oxford University Press 1993, p. 183 – 202
  8. ↑ газета «АиФ». Куда делись символы России?
  9. ↑ Л. М. Сомин. Тайны седого Урала. Малахит
  10. ↑ Mindat map with over 8500 locations

Further reading

Look up malachite in Wiktionary, the free dictionary.
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