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Copper

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Chalcopyrite is the most common copper ore mineral mined today, but not the only one. Copper is one of the few elements that can be found in nature as both a native element, pure or almost pure, (some other native elements are: gold, silver, iron, diamond and sulphur). Several of the minor copper ores, such as malachite and azurite, are also used for jewelry-making. Copper is mined in 50 countries around the world. Chile is the world's largest producer, followed by the United States. These two countries accounted for 46% of total world production. Copper is one of the metals that is both widely used and commonly recycled. Copper like iron and aluminum is vital to every day living. Most of us are in contact with copper or a copper-containing object at all times. Copper has excellent heat and electrical conductive properties, as well as good malleability and ductility characteristics, which make it one of the most widely used and versatile metals in the world. It can be used as a stand-alone material, or in alloy with other metals. Like iron, copper and its alloys bronze and brass have played a major role in the development of modern civilization. Man first used copper in its native form before history was recorded. Copper and copper alloys have played critical roles in the development of civilization as we have come to know it.

Chalcopyrite Azurite Azurite

Chemistry: Cu, Elemental Copper

Native copper (copper found in a chemically uncombined state) has been mined since ancient times and now is essentially depleted as an economically viable ore. It is commonly associated with basic extrusive igneous rocks where copper has formed by reaction between copper-bearing solutions and iron minerals. In this type of deposit, which has been extensively mined[3] on the Keweenaw Peninsula[1], Michigan, native copper is associated with chalcocite, bornite, epidote, calcite, prehnite, chlorite, zeolites, and small amounts of native silver. In the Keweenaw deposits, copper was recovered and used by native peoples and early settlers[2]. From 1845 to the present, approximately 100 mining companies have produced copper from these deposits; since 1900 the deposits have become less important as a source of copper, and the district is now mostly exhausted.

Most copper today is recovered from sulphides and from the oxidized minerals (oxides, carbonates, sulphides). Metallic copper is used for wiring, electrical components, coins, tubing and many other applications. Native copper is still found in limited quantities in once-active mining regions. These finds are now valuable as mineralogical specimens and ornamental pieces. Fine specimens only rarely demonstrate crystal faces and these are prized above otherwise similar specimens.
References:
[1] [ Keweenaw NHP Home Page: http://www.nps.gov/kewe ]
[2] [ Copper Mining History & Copper Harbor Michigan: http://www.exploringthenorth.com/ ]
[3] [ Copper Mining Gallery Tour, Michigan Historical Museum: http://www.michigan.gov/sos ]

Physical Characteristics
  • Color: copper-colored; weathered specimens tarnished green.
  • Luster: metallic.
  • Transparency: opaque.
  • Crystal System: isometric.
  • Crystal Habits include: massive, wires and arborescent or branching forms as the most common, whole individual crystals are extremely rare but when present are usually cubes and octahedrons. Occasionally, massive forms will show some recognizable crystal faces on outer surfaces.
  • Cleavage: absent.
  • Fracture: jagged.
  • Streak: reddish copper color.
  • Hardness: 2.5-3
  • Specific Gravity: 8.9+
  • Associated Minerals: silver, calcite, malachite and other secondary copper minerals.
Notable Occurrences include Michigan and Arizona, USA; Germany; Russia and Australia. Best Field Indicators are color, ductility and crystal habit.

CuFeS2, Copper Iron Sulfide

  • Class: Sulfides
  • Group: Chalcopyrite
  • Uses: Major ore of copper
Chalcopyrite (or copper pyrite), looks like, and is easily confused with Pyrite, FeS2. Chalcopyrite is one of the minerals referred to as "Fool's Gold" because of its bright golden color. But real gold is a more buttery yellow and is ductile and malleable.
As an ore of copper, the yield of chalcopyrite is rather low in terms of atoms per molecule. It is only 25%, compared to other copper minerals such as chalcocite, Cu2S-67%; cuprite, Cu2O-67%; covellite, CuS-50% or bornite Cu5FeS4-50%. However the large quantities and widespread distribution of chalcopyrite make it the leading source of copper. Chalcopyrite is a common mineral and is found in almost all sulfide deposits.

Physical Characteristics
  • Color: brassy yellow, tarnishes to iridescent blues, greens, yellows and purples.
  • Luster: metallic.
  • Transparency: Crystals are opaque.
  • Crystal System: tetragonal.
  • Crystal Habits: predominantly the disphenoid which is like two opposing wedges and resembles a tetrahedron.
  • Cleavage: poor
  • Fracture: conchoidal and brittle.
  • Hardness: 3.5-4
  • Specific Gravity: 4.2
  • Streak: dark green.
  • Other Characteristics: Some striations on most crystal faces.
  • Associated Minerals: quartz, fluorite, barite, dolomite, calcite, pentlandite, pyrite and other sulfides.
Notable Occurrences include Canada, Chile, Peru, Mexico, Europe, South Africa, several USA sites and many others around the world.

Azurite

Chemistry: Cu3(CO3)2(OH)2

  • Copper Carbonate Hydroxide.
  • Class: Carbonates.
  • Uses: ornamental stone, pigment, minor ore of copper, and jewelry.
Azurite is a very popular mineral because of its unparalleled color, a deep blue called "azure", hence its name. The color is due to the presence of copper (a strong coloring agent), and the way the copper chemically combines with the carbonate groups (CO3) and hydroxyls (OH). Azurite has been used as a dye for paints and fabrics since ancient times.

Malachite (see below) is closely associated with azurite in many ways. Not only do they frequently occur together, they also have very similar formulae (a difference in structure produces the green color for malachite). Malachite can also replace azurite, making a pseudomorph, or an exact copy of an azurite crystal (except for the now-green color).

Azurite is used in jewelry and for dyes as mentioned above. It is also an unimportant ore of copper. Fine crystal clusters, nodular specimens, and interesting and beautiful combinations with malachite are important pieces in anyone's mineral collection.

Physical Characteristics
  • Color is azure, deep blue or pale blue if found in small crystals or crusts.
  • Luster is vitreous to dull depending on habit.
  • Transparency: transparent if in thin crystals, otherwise translucent to opaque.
  • Crystal System is monoclinic; 2/m
  • Crystal Habits: irregular blades with wedge shaped terminations.
  • Aggregate crusts and radiating: botryoidal, nodular and earthy masses.
  • Cleavage: good
  • Fracture: conchoidal and brittle.
  • Hardness: 3.5-4
  • Specific Gravity: 3.7+
  • Streak: blue.
Associated Minerals are limonite, chalcopyrite, native copper, calcite, cuprite, chrysocolla, malachite and other oxidized copper minerals. Notable Occurrences include numerous localities in southwestern USA; Mexico; Nambia; Zaire; Morocco; Australia and in Europe.

Chemistry: Cu2(CO3)(OH)2

  • Copper Carbonate Hydroxide.
  • Class: Carbonate.
  • Uses: Minor ore of copper, ornamental stone, pigment, and jewelry.
Malachite is a famous and very popular semi-precious stone. Its banded light and dark green designs are one-of-a-kind, and give it a unique ornamental quality unlike that of any other stone. Although its massive forms are well known, its crystalline forms are rare.

Physical Characteristics
  • Color is banded light and dark green or (if crystalline), just dark green.
  • Luster: dull in massive forms and silky as crystals.
  • Transparency: opaque in massive form and translucent in crystalline forms.
  • Crystal System: monoclinic;
  • Crystal Habits: in its massive forms are botryoidal, stalactitic or globular. Crystals are acicular or fibrous and form in tufts and encrustations.
  • Cleavage: good in one direction but rarely seen.
  • Fracture: conchoidal to splintery.
  • Hardness: 3.5-4
  • Specific Gravity: 3.9+
  • Streak: green.
  • Associated Minerals include limonite, chalcopyrite, native copper, calcite, cuprite, azurite, chrysocolla, and other copper deposit minerals.
  • Other Characteristics: weakly effervesces in acid
Notable Occurrences include Zaire; Nambia; Ural mountains, Russia, Australia, England, and Arizona, USA.

For more information about copper, any of its minerals or just general questions about the earth sciences try some of these links:
International Copper Association: http://www.copper.org
Geological Timescale: http://www.geo.ucalgary.ca/~macrae/
United States Geological Survey (USGS): http://www.usgs.gov/
Minerals by name: http://mineral.galleries.com/
Minerals Yearbook: http://minerals.er.usgs.gov/

Azurite Chalcopyrite Tarnished Chalcopyrite
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