Chalcopyrite

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Chalcopyrite

General
Category	Mineral
Chemical formula	copper iron sulfide:CuFeS₂
Identification
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
Refractive index	opaque
Streak	dark green
Specific gravity	4.1 - 4.3
Solubility	Soluble in HNO₃
Other Characteristics	magnetic on heating

Chalcopyrite 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.

1 Identification
2 Chemistry
3 Paragenesis
4 Occurrence
5 References

[edit] 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 lustre.

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

[edit] 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 ad 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, etcetera.

[edit] 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.

[edit] Occurrence

Chalcopyrite is one of the most important copper ores. 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.