Malachite

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Malachite
Malachite, Zaire.jpg
Malachite from the Democratic Republic of the Congo
General
Category Carbonate mineral
Formula
(repeating unit)		Cu2CO3(OH)2
IMA symbol Mlc [1]
Strunz classification 5.BA.10
Crystal system Monoclinic
Crystal class Prismatic (2/m)
(same H-M symbol)
Space group P21/a
Identification
Formula mass 221.1 g/mol
ColorBright green, dark green, blackish green, with crystals deeper shades of green, even very dark to nearly black commonly banded in masses; green to yellowish green in transmitted light
Crystal habit Massive, botryoidal, stalactitic, crystals are acicular to tabular prismatic
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 hardness3.5–4
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 propertiesBiaxial (–)
Refractive index nα = 1.655 nβ = 1.875 nγ = 1.909
Birefringence δ = 0.254
References [2] [3] [4] [5]

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 deep, underground spaces, where the water table and hydrothermal fluids provide the means for chemical precipitation. Individual crystals are rare, but occur as slender to acicular prisms. Pseudomorphs after more tabular or blocky azurite crystals also occur. [5]

Contents

Etymology and history

The entrance to the Neolithic era malachite mine complex on the Great Orme, Wales Great Orme Copper Mine - geograph.org.uk - 819.jpg
The entrance to the Neolithic era malachite mine complex on the Great Orme, Wales

The stone's name derives (via Latin : molochītis, Middle French : melochite, and Middle English melochites) from Greek Μολοχίτης λίθος molochites lithos, "mallow-green stone", from μολόχη molochē, variant of μαλάχη malāchē, "mallow". [6] The mineral was given this name due to its resemblance to the leaves of the mallow plant. [7] Copper (Cu2+) gives malachite its green color. [8]

Malachite was mined from deposits near the Isthmus of Suez and the Sinai as early as 4000 BCE. [9]

It was extensively mined at the Great Orme Mines in Britain 3,800 years ago, using stone and bone tools. Archaeological evidence indicates that mining activity ended c. 600 BCE, with up to 1,760 tonnes of copper being produced from the mined malachite. [10] [11]

Archaeological evidence indicates that the mineral has been mined and smelted to obtain copper at Timna Valley in Israel for more than 3,000 years. [12] Since then, malachite has been used as both an ornamental stone and as a gemstone.

The use of azurite and malachite as copper ore indicators led indirectly to the name of the element nickel in the English language. Nickeline, a principal ore of nickel that is also known as niccolite, weathers at the surface into a green mineral (annabergite) that resembles malachite. This resemblance resulted in occasional attempts to smelt nickeline in the belief that it was copper ore, but such attempts always ended in failure due to high smelting temperatures needed to reduce nickel. In Germany this deceptive mineral came to be known as kupfernickel, literally "copper demon." The Swedish alchemist Baron Axel Fredrik Cronstedt (who had been trained by Georg Brandt, the discoverer of the nickel-like metal cobalt) realized that there was probably a new metal hiding within the kupfernickel ore, and in 1751 he succeeded in smelting kupfernickel to produce a previously unknown (except in certain meteorites) silvery white, iron-like metal. Logically, Cronstedt named his new metal after the nickel part of kupfernickel.

Occurrence

Malachite in the walls of Outokumpu's old mine. Outokumpu malachite.jpg
Malachite in the walls of Outokumpu's old mine.

Malachite often results from the supergene weathering and oxidation of primary sulfidic copper ores, and is often found 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, [13] but G.N Vertushkova reports the possible discovery of new deposits of malachite in the Urals. [14] It is found worldwide including in the Democratic Republic of the Congo; Gabon; Zambia; Tsumeb, Namibia; Mexico; Broken Hill, New South Wales; Burra, South Australia; Lyon, France; Timna Valley, Israel; and the Southwestern United States, most notably in Arizona. [15]

Structure

Malachite crystallizes in the monoclinic system. The structure consists of chains of alternating Cu2+ ions and OH− ions, with a net positive charge, woven between isolated triangular CO32− ions. Thus each copper ion is conjugated to two hydroxyl ions and two carbonate ions; each hydroxyl ion is conjugated with two copper ions; and each carbonate ion is conjugated with six copper ions. [16] [17]

Use

The funerary mask of the Red Queen of Palenque is made from a mosaic of malachite. Ajuar funerario de la Reina Roja - 8.jpg
The funerary mask of the Red Queen of Palenque is made from a mosaic of malachite.

Malachite was used as a mineral pigment in green paints from antiquity until c. 1800. [19] The pigment is moderately lightfast, sensitive to acids, and varying in color. This natural form of green pigment has been replaced by its synthetic form, verditer, among other synthetic greens.

Malachite is also used for decorative purposes, such as in wands and the Malachite Room in the Hermitage Museum, [20] which features a huge malachite vase, and the Malachite Room in Castillo de Chapultepec in Mexico City. [21] Another example is the Demidov Vase, part of the former Demidov family collection, and now in the Metropolitan Museum of Art. [22] "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 centre of the room of Linda Hall Library. In the time of Tsar Nicolas I decorative pieces with malachite were among the most popular diplomatic gifts. [23] It was used in China as far back as the Eastern Zhou period. [24] The base of FIFA World Cup Trophy has two layers of malachite.

Symbolism and superstitions

A 17th-century Spanish superstition held that having a child wear a lozenge of malachite would help them sleep, and keep evil spirits at bay. [25] Marbodus recommended malachite as a talisman for young people because of its protective qualities and its ability to help with sleep. [26] It has also historically been worn for protection from lightning and contagious diseases and for health, success, and constancy in the affections. [26] During the Middle Ages it was customary to wear it engraved with a figure or symbol of the Sun to maintain health and to avert depression to which Capricorns were considered vulnerable. [26]

In ancient Egypt the colour green (wadj) was associated with death and the power of resurrection as well as new life and fertility. Ancient Egyptians believed that the afterlife contained an eternal paradise, referred to as the "Field of Malachite", which resembled their lives but with no pain or suffering. [27]

Ore uses

Copper nugget example Natural copper nugget.jpg
Copper nugget example

Simple methods of copper ore extraction from malachite involved thermodynamic processes such as smelting. [28] This reaction involves the addition of heat and a carbon, causing the carbonate to decompose leaving copper oxide and an additional carbon source such as coal converts the copper oxide into copper metal. [28] [29]

The basic word equation for this reaction is:

Copper carbonate + heat → carbon dioxide + copper oxide (color changes from green to black). [28] [29]

Copper oxide + carbon → carbon dioxide + copper (color change from black to copper colored). [28] [29]

Malachite is a low grade copper ore, however, due to increase demand for metals, more economic processing such as hydrometallurgical methods (using aqueous solutions such as sulfuric acid) are being used as malachite is readily soluble in dilute acids. [30] [31] Sulfuric acid is the most common leaching agent for copper oxide ores like malachite and eliminates the need for smelting processes. [32]

The chemical equation for sulfuric acid leaching of copper ore from malachite is as follows: [32]

malachiteCu2(OH)2CO3 + sulfuric acid2H2SO4 → copper sulfate2CuSO4 + carbon dioxideCO2 + water3H2O

 

 

 

 

(Reaction 1)

Health and environmental concerns

Mining for malachite for ornamental or copper ore purposes involves open-pit mining or underground mining depending on the grade of the ore deposits. [33] Open-pit and underground mining practices can cause environmental degradation through habitat and biodiversity loss. [34] [35] Acid mine drainage can contaminate water and food sources to negatively impact human health if improperly managed or if leaks from tailing ponds occur. [35] [36] The risk of health and environmental impacts of both traditional metallurgy and newer methods of hydrometallurgy are both significant, [35] however, water conservation and waste management practices for hydrometallurgy processes for ore extraction, such as for malachite, are stricter and relatively more sustainable. [37] New research is also being conducted on better alternatives to methods such as sulfuric acid leaching which has high environmental impacts, even under hydrometallurgy regulation standards and innovation. [32]

See also

Related Research Articles

Bioleaching is the extraction or liberation of metals from their ores through the use of living organisms. Bioleaching is one of several applications within biohydrometallurgy and several methods are used to treat ores or concentrates containing copper, zinc, lead, arsenic, antimony, nickel, molybdenum, gold, silver, and cobalt.

<span class="mw-page-title-main">Ore</span> Rock with valuable metals, minerals and elements

Ore is natural rock or sediment that contains one or more valuable minerals concentrated above background levels, typically containing metals, that can be mined, treated and sold at a profit. The grade of ore refers to the concentration of the desired material it contains. The value of the metals or minerals a rock contains must be weighed against the cost of extraction to determine whether it is of sufficiently high grade to be worth mining and is therefore considered an ore. A complex ore is one containing more than one valuable mineral.

<span class="mw-page-title-main">Smelting</span> Use of heat and a reducing agent to extract metal from ore

Smelting is a process of applying heat and a chemical reducing agent to an ore to extract a desired base metal product. It is a form of extractive metallurgy that is used to obtain many metals such as iron, copper, silver, tin, lead and zinc. Smelting uses heat and a chemical reducing agent to decompose the ore, driving off other elements as gases or slag and leaving the metal behind. The reducing agent is commonly a fossil fuel source of carbon, such as carbon monoxide from incomplete combustion of coke—or, in earlier times, of charcoal. The oxygen in the ore binds to carbon at high temperatures as the chemical potential energy of the bonds in carbon dioxide is lower than that of the bonds in the ore.

<span class="mw-page-title-main">Limonite</span> Hydrated iron oxide mineral

Limonite is an iron ore consisting of a mixture of hydrated iron(III) oxide-hydroxides in varying composition. The generic formula is frequently written as FeO(OH)·nH2O, although this is not entirely accurate as the ratio of oxide to hydroxide can vary quite widely. Limonite is one of the three principal iron ores, the others being hematite and magnetite, and has been mined for the production of iron since at least 2500 BP.

Extractive metallurgy is a branch of metallurgical engineering wherein process and methods of extraction of metals from their natural mineral deposits are studied. The field is a materials science, covering all aspects of the types of ore, washing, concentration, separation, chemical processes and extraction of pure metal and their alloying to suit various applications, sometimes for direct use as a finished product, but more often in a form that requires further working to achieve the given properties to suit the applications.

<span class="mw-page-title-main">Chalcopyrite</span> Copper iron sulfide mineral

Chalcopyrite ( KAL-kə-PY-ryte, -⁠koh-) is a copper iron sulfide mineral and the most abundant copper ore mineral. It has the chemical formula CuFeS2 and crystallizes in the tetragonal system. It has a brassy to golden yellow color and a hardness of 3.5 to 4 on the Mohs scale. Its streak is diagnostic as green-tinged black.

<span class="mw-page-title-main">Basic copper carbonate</span> Chemical compound

Basic copper carbonate is a chemical compound, more properly called copper(II) carbonate hydroxide. It is an ionic compound consisting of the ions copper(II) Cu2+
, carbonate CO2−
3, and hydroxide OH−
.

<span class="mw-page-title-main">Galena</span> Natural mineral form of lead sulfide

Galena, also called lead glance, is the natural mineral form of lead(II) sulfide (PbS). It is the most important ore of lead and an important source of silver.

<span class="mw-page-title-main">Azurite</span> Copper carbonate mineral

Azurite is a soft, deep-blue copper mineral produced by weathering of copper ore deposits. During the early 19th century, it was also known as chessylite, after the type locality at Chessy-les-Mines near Lyon, France. The mineral, a basic carbonate with the chemical formula Cu3(CO3)2(OH)2, has been known since ancient times, and was mentioned in Pliny the Elder's Natural History under the Greek name kuanos (κυανός: "deep blue," root of English cyan) and the Latin name caeruleum. Copper (Cu2+) gives it its blue color.

<span class="mw-page-title-main">Nickeline</span> Nickel arsenide mineral

Nickeline or niccolite is a mineral consisting primarily of nickel arsenide (NiAs). The naturally-occurring mineral contains roughly 43.9% nickel and 56.1% arsenic by mass, but composition of the mineral may vary slightly.

<span class="mw-page-title-main">Copper extraction</span> Process of extracting copper from the ground

Copper extraction refers to the methods used to obtain copper from its ores. The conversion of copper ores consists of a series of physical, chemical and electrochemical processes. Methods have evolved and vary with country depending on the ore source, local environmental regulations, and other factors.

<span class="mw-page-title-main">Aurichalcite</span> Basic carbonate of zinc and copper

Aurichalcite is a carbonate mineral, usually found as a secondary mineral in copper and zinc deposits. Its chemical formula is (Zn,Cu)5(CO3)2(OH)6. The zinc to copper ratio is about 5:4. Copper (Cu2+) gives aurichalcite its green-blue colors.

<span class="mw-page-title-main">Dioptase</span>

Dioptase is an intense emerald-green to bluish-green copper cyclosilicate mineral. It is transparent to translucent. Its luster is vitreous to sub-adamantine. Its formula is Cu6Si6O18·6H2O (also reported as CuSiO2(OH)2). It has a hardness of 5, the same as tooth enamel. Its specific gravity is 3.28–3.35, and it has two perfect and one very good cleavage directions. Additionally, dioptase is very fragile, and specimens must be handled with great care. It is a trigonal mineral, forming 6-sided crystals that are terminated by rhombohedra.

Hydrometallurgy is a technique within the field of extractive metallurgy, the obtaining of metals from their ores. Hydrometallurgy involve the use of aqueous solutions for the recovery of metals from ores, concentrates, and recycled or residual materials. Processing techniques that complement hydrometallurgy are pyrometallurgy, vapour metallurgy, and molten salt electrometallurgy. Hydrometallurgy is typically divided into three general areas:

<span class="mw-page-title-main">Heap leaching</span> Industrial mining process used to extract precious metals from ore

Heap leaching is an industrial mining process used to extract precious metals, copper, uranium, and other compounds from ore using a series of chemical reactions that absorb specific minerals and re-separate them after their division from other earth materials. Similar to in situ mining, heap leach mining differs in that it places ore on a liner, then adds the chemicals via drip systems to the ore, whereas in situ mining lacks these liners and pulls pregnant solution up to obtain the minerals. Heap leaching is widely used in modern large-scale mining operations as it produces the desired concentrates at a lower cost compared to conventional processing methods such as flotation, agitation, and vat leaching.

In ore deposit geology, supergene processes or enrichment are those that occur relatively near the surface as opposed to deep hypogene processes. Supergene processes include the predominance of meteoric water circulation (i.e. water derived from precipitation) with concomitant oxidation and chemical weathering. The descending meteoric waters oxidize the primary (hypogene) sulfide ore minerals and redistribute the metallic ore elements. Supergene enrichment occurs at the base of the oxidized portion of an ore deposit. Metals that have been leached from the oxidized ore are carried downward by percolating groundwater, and react with hypogene sulfides at the supergene-hypogene boundary. The reaction produces secondary sulfides with metal contents higher than those of the primary ore. This is particularly noted in copper ore deposits where the copper sulfide minerals chalcocite (Cu2S), covellite (CuS), digenite (Cu18S10), and djurleite (Cu31S16) are deposited by the descending surface waters.

The Whim Creek Copper Mine is a copper oxide mine, located in the City of Karratha in the Pilbara region of Western Australia.

<span class="mw-page-title-main">Cobalt</span> Chemical element, symbol Co and atomic number 27

Cobalt is a chemical element; it has symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, produced by reductive smelting, is a hard, lustrous, silvery metal.

<span class="mw-page-title-main">Pseudomalachite</span>

Pseudomalachite is a phosphate of copper with hydroxyl, named from the Greek for "false" and "malachite", because of its similarity in appearance to the carbonate mineral malachite, Cu2(CO3)(OH)2. Both are green coloured secondary minerals found in oxidised zones of copper deposits, often associated with each other. Pseudomalachite is polymorphous with reichenbachite and ludjibaite. It was discovered in 1813. Prior to 1950 it was thought that dihydrite, lunnite, ehlite, tagilite and prasin were separate mineral species, but Berry analysed specimens labelled with these names from several museums, and found that they were in fact pseudomalachite. The old names are no longer recognised by the IMA.

<span class="mw-page-title-main">Cobalt extraction</span>

Cobalt extraction refers to the techniques used to extract cobalt from its ores and other compound ores. Several methods exist for the separation of cobalt from copper and nickel. They depend on the concentration of cobalt and the exact composition of the ore used.

References

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  2. ↑ Mineralienatlas
  3. ↑ Anthony, John W.; Bideaux, Richard A.; Bladh, Kenneth W.; Nichols, Monte C., eds. (2003). "Malachite" (PDF). Handbook of Mineralogy. Vol. V (Borates, Carbonates, Sulfates). Chantilly, Virginia: Mineralogical Society of America. ISBN   0962209740.
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  5. 1 2 Malachite. Mindat
  6. ↑ Malachite, Dictionary.com
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  8. ↑ "Minerals Colored by Metal Ions". minerals.gps.caltech.edu. Retrieved 2023-03-01.
  9. ↑ Susarla, S.M (2016). "The colourful history of malachite green: from ancient Egypt to modern surgery". International Journal of Oral and Maxillofacial Surgery. 46 (3): 401–403. doi:10.1016/j.ijom.2016.09.022. PMID   27771151.
  10. ↑ Johnson, Ben, ed. (2014). "The Great Orme Mines" . Retrieved 2017-06-06.
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  13. ↑ Куда делись символы России? Archived 2013-12-02 at the Wayback Machine Argumenty i Fakty (24 May 2006)
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  21. ↑ Budrina, Ludmila (January 2013). "La produzione in malachite dei Demidov: sulle trace degli oggetti alla prima esposizione universale / I Demidoff fra Russia e Italia. Gusto e prestigio di une famiglia in Europa dal XVIII al XX secolo. – P. 151-176, 9 tav". // I Demidoff Fra Russia e Italia. Gusto e Prestigio di Une Famiglia in Europa Dal XVIII al XX Secolo. A Cura di Lucia Tonini. Cultura e Memoria, Vol. 50. – Firenze: Leo S. Olschki, 2013.
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  27. ↑ Hill, J (2010). "Meaning of green in ancient Egypt". Ancient Egypt Online. Retrieved 2016-11-28.
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  29. 1 2 3 Day, Jo; Kobik, Maggie (2019-09-30), "Reconstructing a Bronze Age Kiln from Priniatikos Pyrgos, Crete", Experimental Archaeology: Making, Understanding, Story-telling, Archaeopress Publishing Ltd, pp. 63–72, doi:10.2307/j.ctvpmw4g8.11, ISBN   978-1-78969-320-1, S2CID   210629355 , retrieved 2021-02-25
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  37. ↑ Conard, Bruce R. (1992-06-01). "The role of hydrometallurgy in achieving sustainable development". Hydrometallurgy. Hydrometallurgy, Theory and Practice Proceedings of the Ernest Peters International Symposium. Part B. 30 (1): 1–28. Bibcode:1992HydMe..30....1C. doi:10.1016/0304-386X(92)90074-A. ISSN   0304-386X.
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