Chalcocite
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Chalcocite is named from the Greek chalkos for copper; for its composition.

Discovered in 1832;   IMA status: Valid (pre-IMA; Grandfathered)

Chemistry

Chemical Formula:

Cu₂S

Copper Sulfate

Molecular Weight:

159.16 gm

Composition:

Copper

79.85 %

Cu

Sulfur

20.15 %

S

100.00 %

Classification

Mineral Classification:

Sulfides

Strunz 8th Ed. ID:

2/B.01-10

Nickel-Strunz 10th Ed. ID:

2.BA.05

2 : SULFIDES and SULFOSALTS (sulfides, selenides, tellurides; arsenides, antimonides, bismuthides; sulfarsenites, sulfantimonites, sulfbismuthites, etc.)
B : Metal Sulfides, M: S > 1: 1 (mainly 2: 1)
A : With Cu, Ag, Au

Related to:

Chalcocite-Digenite Group. Chalcocite-Yarrowite Series.

Members of Group:

Chalcocite-Digenite Group: Chalcocite, Digenite, Djurleite, Roxbyite

Varieties:

Argentiferous Chalcocite, Ducktownite, Harrisite, Para-Kupferglanz

Synonyms:

Chalcocine, Chalcosine, Chalcosite, Copper Glance, Cuprein, Cupreine, Cyprite, Kuprein, Redruthite, Vitreous Copper

Crystal Data

Crystallography:

Monoclinic - Prismatic

Crystal Habit:

Crystals are short prismatic [001], thick to tabular {001}, to 12 cm across, and prismatic [100], to 25 cm long; {001} is striated || [100]. Massive, compact, fine powdery.

Twinning:

Common on {110} yielding pseudohexagonal stellate forms; also on {032}, {112}. Seen as lamellar twinning in polished section.

Physical Properties

Cleavage:

Indistinct on {110}

Fracture:

Conchoidal

Tenacity:

Brittle, somewhat sectile.

Moh's Hardness:

2.5 - 3.0; VHN = 84–87 (100 g load)

Density:

5.50 - 5.80 (g/cm³)

Luminescence:

None

Radioactivity:

Not Radioactive

Optical Properties

Color:

Blue Black, Gray, Black, Black Gray, or steel Gray

Transparency:

Opaque

Luster:

Metallic

Refractive Index:

R1–R2: (400) 37.0–36.8, (420) 37.8–37.4, (440) 37.7–37.6, (460) 37.0–37.2, (480) 36.2–36.2, (500) 35.6–35.4, (520) 34.7–34.4, (540) 33.7–33.5, (560) 32.5–32.5, (580) 32.1–31.8, (600) 31.3–31.2, (620) 30.8–30.7, (640) 30.0–30.0, (660) 29.5–30.0, (680) 29.2–29.7, (700) 29.0–29.6

Birefringence:

None; Opaque

Dispersion:

None

Pleochroism:

None

Anisotrophism:

Weak

Occurances

Geological Setting:

An uncommon primary hydrothermal mineral but important as a secondary mineral. Found in or below the zone of oxidation in hydrothermal veins and in large low-grade porphyry copper orebodies.

Common Associations:

Pyrite, Chalcopyrite, Covellite, Bornite, Molybdenite, many other sulfides and their alteration products.

Common Impurities:

Fe

Co-type Localities:

· Cornwall, England,
· Butte, Montana

Year Discovered:

1832

View mineral photos:

Chalcocite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Chalcocite is an important ore of copper and a secondary mineral in or near the oxidized zone of copper sulfide deposits. It has been mined for centuries and is one of the most profitable copper ores because of its high copper content (nearly 80% by weight) and the ease at which copper can be separated from sulfur. However, it is not the primary ore of copper due to its scarcity. The richest Chalcocite deposits have probably been mined out but it is still being mined. Fine crystals of Chalcocite are quite uncommon and are very sought after. The now depleted mines at Cornwall, England and Bristol, Connecticut produced the most famous clusters of wonderfully formed Chalcocite crystals.

Since Chalcocite is a secondary mineral that forms from the alteration of other minerals, it has been known to form pseudomorphs of many different minerals. A pseudomorph is a mineral that has replaced another mineral atom by atom, but it leaves the original mineral's crystal shape intact. Chalcocite has been known to form pseudomorphs of the minerals Bornite, Covellite, Chalcopyrite, Pyrite, Enargite, Galena and Sphalerite. Pseudo means false and morph means shape or form, thus pseudomorph means false shape since the mineral is Chalcocite but the shape is that of another crystal, Covellite for example.

Distribution: An important and widely distributed ore mineral of copper. Only a few localities producing exceptional crystals or pure masses can be listed. From the Turinsk copper mine, Bogoslovsk, Ural Mountains, Russia. In England, fine crystals from Cornwall at St. Just, St. Ives, Camborne, and Redruth. In the USA, exceptional crystals from Bristol, Hartford County, Connecticut; in Arizona, at Bisbee, Cochise County; from the Magma mine, Superior, Pinal County; in the United Verde Extension mine, Yavapai County; from Butte, Silver Bow County, Montana; crystals at the Flambeau mine, southwest of Ladysmith, Rusk County, Wisconsin; from Kennicott, Copper River district, Alaska. Large crystals from Nababiep West mine, Cape Province, and Messina, Transvaal, South Africa. At M’Passa, Niari Province, Congo Republic. In the Mashamba West mine, Kolwezi, Katanga Province, Congo (Shaba Province, Zaire). Fine crystals from Telfer, Western Australia.
 

  
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