chalcopyrite

[New Latin chalcopyrites : Greek khalkos, copper + PYRITES.]

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A mineral having composition CuFeS₂. Crystals are usually small and resemble tetrahedra. Chalcopyrite is usually massive with a metallic luster, brass-yellow color, and sometimes an iridescent tarnish. The Mohs hardness is 3.5–4.0, and the density 4.1–4.3. Chalcopyrite is a so-called fool's gold, but is brittle while gold is sectile. Pyrite, the most widespread fool's gold, is harder than chalcopyrite. See also Pyrite.

Chalcopyrite is the most widespread primary copper ore mineral. It is commonly found in veins (Braden mine, Chile; Cornwall, England; Butte, Montana; Freiberg, Saxony; Tasmania; Rio Tinto, Spain). Chalcopyrite is also found in contact metamorphic deposits in limestone (Bisbee, Arizona) and as sedimentary deposits (Mansfeld, Germany). See also Copper.

Environment

Common in multitemperature sulfide veins, and often disseminated through porphyritic igneous rocks.

Though tetragonal, the characteristically sphenoidal crystals of chalcopyrite resemble tetrahedra. Crystals of 2-3 cm are common; often they are even larger, with faces usually somewhat uneven and tarnished from black to brilliant iridescent hues. Usually massive, often making up golden sulfide mixtures of several minerals. Structurally close to sphalerite, it often makes oriented intergrowths, with small crystals studded over sphalerite surfaces.

Golden. Luster metallic, often with iridescent tarnish; hardness 3Ɖ-4; gravity 4.1-4.3; fracture uneven; cleavage 1 poor (and rarely noted). Brittle.

Sulfide of copper and iron (34.5% Cu, 30.5% Fe, 35% S).

On charcoal, fuses to magnetic black globule; touched with HCl, tints flame with blue flash. Solution with strong nitric acid is green; ammonia precipitates red iron hydroxide and leaves a blue solution.

Confused with gold, but is brittle, crushes to a green-black powder, gives black streak, and dissolves in acid. Distinguished from pyrite by ease of scratching and by copper tests. The color is a richer yellow than pyrite. Also, obviously hard and shiny pyrite will frequently show smooth flat surfaces, striated cubes or pyritohedrons, whereas chalcopyrite, when not massive, is in characteristic sphenoidal crystals.

The basic copper ore. Widely distributed and may be found in all types of primary occurrences. Often associated with other copper minerals: pyrite, sphalerite, galena, and pyrrhotite. The economically important "porphyry coppers" of Bingham, Utah; Ely, Nevada; and Ajo, Arizona; are representative of open-pit-mined, worldwide low-grade (1-3 percent) copper disseminations through igneous rocks. Some of the best crystals are from Cornwall, England; Akita and Tochigi prefectures, Japan; French Creek, Pennsylvania; and several Colorado localities. Often crystallized in the parallel growths on and through crystals of sphalerite in the Joplin District of Missouri, Kansas, and Oklahoma. Giant 6-in. (15 cm) crystals were found in Freirina, n. Chile. Abundant in n. Mexico, another good source of large crystals.

Chalcopyrite is the generic copper ore that, by alteration and successive removals of iron, produces a series starting with chalcopyrite and going through bornite (Cu ₅ FeS ₄ ), covellite (CuS), and chalcocite (Cu ₂ S), and ending (rarely) as native copper (Cu). (See discussion of secondary enrichment under chalcocite.)

Chalcopyrite
General
Category	Mineral
Chemical formula	copper iron sulfide:CuFeS2
Identification
Molar mass	183.54
Color	Brass yellow, may have iridescent purplish tarnish.
Crystal habit	predominantly the disphenoid and resembles a tetrahedron. Crystals sometines twinned. Also commonly massive, and sometimes botryoidal.
Crystal system	tetragonal bar 4 2m
Cleavage	[112] Indistinct
Fracture	conchoidal and brittle
Mohs scale hardness	3.5
Luster	metallic
Streak	dark green
Specific gravity	4.1 - 4.3
Refractive index	opaque
Solubility	Soluble in HNO3
Other characteristics	magnetic on heating

The unit cell of chalcopyrite. Copper is shown in pink, iron in blue and sulfur in yellow.

Chalcopyrite (pronounced /ˌkælkɵˈpaɪraɪt/ KAL-co-PYE-ryet) is a copper iron sulfide mineral that crystallizes in the tetragonal system. It has the chemical composition CuFeS₂.

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.

On exposure to air, chalcopyrite oxidises to a variety of oxides, hydroxides and sulfates. Associated copper minerals include the sulfides bornite (Cu₅FeS₄), chalcocite (Cu₂S), covellite (CuS), digenite (Cu₉S₅); carbonates such as malachite and azurite, and rarely oxides such as cuprite (Cu₂O). Chalcopyrite is rarely found in association with native copper.

Contents 1 Identification 2 Chemistry 3 Paragenesis 4 Occurrence 5 Generic term 6 Images 7 References

Identification

Chalcopyrite is often confused with pyrite, although the latter has a cubic and not a tetragonal crystal system. Further, chalcopyrite is often massive, rarely crystalline, and less brittle. Chalcopyrite is also a darker yellow in color, with a greenish tinge and diagnostic greasy luster.

Due to its color and high copper content, chalcopyrite has often been referred to as "yellow copper".

Chemistry

Natural chalcopyrite has no solid solution series with any other sulfide minerals. There is limited substitution of Zn with Cu despite chalcopyrite having the same crystal structure as sphalerite.

However, it is often contaminated by a variety of other trace elements such as Co, Ni, Mn, Zn and Sn substituting for Cu and Fe. Se, Fe and As substitute for sulfur, and trace amounts of Ag, Au, Pt, Pd, Pb, V, Cr, In, Al and Sb are reported.

It is likely many of these elements are present in finely intergrown minerals within the chalcopyrite crystal, for instance lamellae of arsenopyrite representing As, molybdenite representing Mo, etc.

Paragenesis

Chalcopyrite is present within many ore bearing environments via a variety of ore forming processes.

Chalcopyrite is present in volcanogenic massive sulfide ore deposits and sedimentary exhalative deposits, formed by deposition of copper during hydrothermal circulation. Chalcopyrite is concentrated in this environment via fluid transport.

Porphyry copper ore deposits are formed by concentration of copper within a granite stock during the ascent and crystallisation of a magma. Chalcopyrite in this environment is produced by concentration within a magma system.

Chalcopyrite is an accessory mineral in Kambalda type komatiitic nickel ore deposits, formed from an immiscible sulfide liquid in sulfur-saturated ultramafic lavas. In this environment chalcopyrite is formed by a sulfide liquid stripping copper from an immiscible silicate liquid.

Chalcopyrite carved owl on a base of quartz crystals, 2.5 inches (6 cm) high.

Occurrence

Chalcopyrite is the most important copper ore. Chalcopyrite ore occurs in a variety of ore types, from huge masses as at Timmins, Ontario, to irregular veins and disseminations associated with granitic to dioritic intrusives as in the porphyry copper deposits of Broken Hill, the American cordillera and the Andes.

Chalcopyrite is present in the supergiant Olympic Dam Cu-Au-U deposit in South Australia.

Chalcopyrite may also be found in coal seams associated with pyrite nodules, and as disseminations in carbonate sedimentary rocks.

Generic term

In Solid State Physics, Chalcopyrite is sometime used as a generic term for any I(A/B)-III-C₂ compound, with C a chalcogenide

Images

Chalcopyrite has a variety of forms and colors:

"Blister Copper" variety of chalcopyrite from Redruth, Cornwall, United Kingdom.

Chalcopyrite with heavy tarnish

Chalcopyrite from Grube Georg, Westerwald, Germany. Image from a display in the Mineralogical Museum, Bonn, Germany.

References

• Dana's Manual of Mineralogy ISBN 0-471-03288-3
• mindat.org
• Webmineral.com
• Mineral Galleries

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