• Chemistry: Cu2S, Copper Sulfide
  • Class: Sulfides
  • Uses: As a minor ore of copper and as mineral specimens.
  • Specimens

Chalcocite is an important copper mineral ore. It has been mined for centuries and is one of the most profitable copper ores. The reasons for this is its high copper content (67% atomic ratio and nearly 80% by weight) and the ease at which copper can be separated from sulfur. It is not however the primary ore of copper due to its scarcity. Although the richest chalcocite deposits have probably been mined out, it is still being mined and will almost certainly always be mined in the future.

Chalcocite occurs as a secondary mineral in many ore bodies in a zone called the supergene enrichment zone. Called a secondary enrichment mineral, although also a primary mineral as well, chalcocite commonly forms from the alteration of primary copper minerals that are attacked above the water table by oxygen. The oxygenated copper fluids descend to the water table where a reaction with primary ores results in the copper being reduced back to a sulfide, most commonly chalcocite. Ore bodies will have a layer of chalcocite which corresponds to the present or a past water table level and this layer is called a "chalcocite blanket". The chalcocite blanket is richer in copper than the upper oxidized portion of the ore body and usually richer than the primary unaltered ores below. The chalcocite blanket represents a real gold mine, or should that be copper mine, to the copper prospectors.

Fine crystals of chalcocite are quite uncommon and are much sought after. The now depleted mines at Cornwall, England and Bristol, Connecticut produced the most famous clusters of wonderfully formed chalcocite crystals. Some new localities with well formed crystals are promising, but so far the specimens from those old mines are the only good chalcocite crystals available on the market. The heavily striated pseudohexagonal tabular crystals are real classics for the mineral collector and often command an equally classic price.

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, millerite, 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 a covellite crystal, for example.


  • Color is dark gray to black.
  • Luster is metallic.
  • Transparency: Crystals are opaque.
  • Crystal System is orthorhombic; 2/m 2/m 2/m below 105 degrees celsius and hexagonal; 6/m 2/m 2/m above 105 degrees celsius.
  • Crystal Habits include pseudohexagonal tabular to prismatic crystals often with a shallow pyramidal truncation with a flat point. Also found massive and compact. Twinning is common and sometimes results in a six pointed star shaped cyclic twin called a trilling or in elbow shaped twins.
  • Cleavage is imperfect in two directions, prismatically.
  • Fracture is conchoidal.
  • Hardness is 2.5 - 3
  • Specific Gravity is approximately 5.5 - 5.8 (above average for metallic minerals)
  • Streak is shiny black to lead gray.
  • Other Characteristics: Crystals are usually deeply grooved with lateral striations and a tarnish will tend to dull the luster of crystals over time.
  • Associated Minerals are quartz, enargite, malachite, azurite, copper, cuprite, tetrahedrite, bornite, tennantite, chalcopyrite, covellite, pyrite and other sulfides.
  • Notable Occurrences include Bristol, Connecticut, Butte, Montana, Morenci and Bisbee, Arizona and Bingham Canyon, Utah, Ducktown, Tennessee, USA; Cornwall, England; Tsumeb, Namibia; Tuscany, Italy and Rio Tinto, Spain.
  • Best Field Indicators are crystal habit, streak, striations, color and associations.
CHALCOCITE specimens:
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CHALCOCITE specimen ccc-1
$ 34.00
Dims: 1.0 x 0.9 x 0.9" (2.5 x 2.3 xc 2.3 cm)
Wt: 26.3 g w/ base
Bristol, Connecticut, U.S.A.
This thumbnail specimen consists of a cluster of many heavily-intergrown Chalcocite crystals. These crystals are in good-to-fair condition, showing several small areas of fresh breakage, and do not appear to exceed 0.3" (8 mm) in length. Their monoclinic prismatic form is not very good due to their intense intergrowth, but a few more or less individual crystals are present. All have a uniform dark gray coloration and a dull metallic luster. There is no host rock of any sort present, and the piece is hot-glued to a flat, square acrylic base.
no photo
ccc-1 ($ 34.00)
Bristol, Connecticut, U.S.A.
CHALCOCITE specimen ccc-2
$ 48.00
Dims: 1.6 x 1.4 x 1.2" (4.1 x 3.6 x 3.0 cm)
Wt: 2.34 oz. (66.4 g)
Bristol, Connecticut, U.S.A.
Dozens of small Chalcocite crystals extend from the massive Chalcocite base of this specimen. These crystals do not appear to exceed 0.3" (8 mm) in length or width, and though they are in good condition, they are incomplete due to their intergrowth with the massive base. Their monoclinic form is good, though, where visible- edges are generally well-defined and faces are clean. All have a moderate gray color and a dull metallic luster, but damage surfaces on the piece show a deep, iridescent blue coloration and a brighter metallic luster. There are a few tiny calcite or cerussite crystals nestled in some crevices and some more massive material in a few spots.
no photo
ccc-2 ($ 48.00)
Bristol, Connecticut, U.S.A.
CHALCOCITE specimen ccc-3
$ 25.00
Dims: 2.5 x 2.1 x 1.4" (6.4 x 5.2 x 3.6 cm)
Wt: 4.5 oz. (127 g)
Dzezkazgan, Dzezkazgan Region, Kazakhstan
At least 20 Chalcocite crystals rest on the gray base rock of this small cabinet specimen. These crystals are generally in good condition- a few are damaged or broken- and do not exceed 0.2" (5 mm) in length or diameter. Their orthorhombic form is rather heavily rounded, but one can still see some pseudohexagonal form and even evidence of some twinning. All have a black color and a dull, nearly submetallic luster. They are accompanied by several small quartz crystals that are in moderately good condition.
no photo
ccc-3 ($ 25.00)
Dzezkazgan, Dzezkazgan Region, Kazakhstan
CHALCOCITE specimen ccc-4
$ 225.00
Dims: 3.8x1.5x2.1" (9.6x3.9x5.3 cm)
Wt: 14.1 oz. (401 g)
Flambeau Mine, 970 Ft. Level, Ladysmith, Rusk County, Wisconsin, USA
This hand specimen is all chalcocite which has uniformly tarnished to a metallic blue color with hints of purple in some areas. A variety of crystal forms are visible, including pseudo-hexagonal prismatic, pseudo-hexagonal tabular, and some crystals that almost look like metallic garnets. The irridescent blue tarnish is very appealing and make it easy to identify the areas of damage (the bottom and a few small areas along the top of the specimen), as these areas are not tarnished, and are a metallic gray color.
no photo
ccc-4 ($225.00)
Flambeau Mine, 970 Ft. Level, Ladysmith, Rusk County, Wisconsin, USA
CHALCOCITE specimen ccc-5
$ 55.00
Dims: 1.75x1.25x1.15" (4.5x3.2x2.9 cm)
Wt: 4.05 oz. (114.5g)
Flambeau Mine, 970 Ft. Level, Ladysmith, Rusk County, Wisconsin, USA
This small specimen of chalcocite is a beautiful irridescent blue, changing to purple from certain angles. The crystal form of the chalcocite is typical with a rounded dome habit. The specimen is only damaged along its base and back, where it was separated from its host.
no photo
ccc-5 ($ 55.00)
Flambeau Mine, 970 Ft. Level, Ladysmith, Rusk County, Wisconsin, USA
CHALCOCITE specimen ccc-6
$ 70.00
Dims: 1.10x0.83x0.63" (2.8x2.1x1.6cm)
Wt: 0.56oz. (15.5g)
Ladysmith, Rusk County, Wisconsin, USA
This is a fine chalcocite specimen from an old collection, and originally came from the Lucky Freddy Flambeau Mine. The specimen is a cluster of a dozen or so chalcocite crystals, all of which have a metallic purple color with irridescent hues of several other colors. The crystals are undamaged, and are typical of chalcocite in appearance.
no photo
ccc-6 ($ 70.00)
Ladysmith, Rusk County, Wisconsin, USA
CHALCOCITE specimen ccc-10
$ 50.00
Dims: 3.09x2.06x1.01" (7.84x5.22x2.56cm)
Wt: 4.85oz (137.2g)
Dzhezkazgan mine, Kazakhstan
On this specimen, the host rock is nearly covered on one surface with chalcocite crystals. They range in size up to 13mm, and have a dark gray color and metallic luster. The crystals are all distorted and show only strong hints of a hexagonal cross section, although many of them show characteristic blunt terminations and all show strong striations. There are other minerals present, both tiny quartz crystals, many golden chalcopyrite crystals, and several patches of tiny blue metallic crystals that look like bornite (they could, of course, be more chalcocite tarnished blue, but then why would the large crystals not have a blue tarnish?).
no photo
ccc-10 ($ 50.00)
Dzhezkazgan mine, Kazakhstan
CHALCOCITE specimen ccc-7
$ 150.00
Dims: 1.44x1.20x0.71" (3.66x3.04x1.81cm)
Wt: 1.38oz (39.2g)
Flambeau mine, Rocket Pocket, Ladysmith, Rusk County, Wisconsin, USA
This is a beautiful specimen of irridescent chalcocite - the pictures can't do it justice. The individual crystals can be identified because each of them displays a different irridescent color, according to their orientation. These colors include blues, violets, purples, and golds. There is one crystal that is pseudo-hexagonal, looking a little bit like a shallow tetrahedron (upside down), but with the points replaced with short faces.
no photo
ccc-7 ($150.00)
Flambeau mine, Rocket Pocket, Ladysmith, Rusk County, Wisconsin, USA
CHALCOCITE specimen ccc-8
$ 25.00
Dims: 1.43x0.93x0.49" (3.63x2.36x1.26cm)
Wt: 0.98oz (27.7g)
Flambeau mine, Rocket Pocket, Ladysmith, Rusk County, Wisconsin, USA
This is an incomplete cluster/crystal of chacocite. I suspect that the original specimen was fractured into two roughly equal parts, and this piece is essentially complete and undamaged except for the smooth, conchoidal fracture that terminates one side of the specimen. The original surfaces have the typicalmetallic luster and suface pattern due to thousands of crystal faces, all deeply striated, that provide the appealing texture of good chalcocite crystals. The fracture surface, however, is relatively smooth (but not perfectly so). All of the surfaces are irridescent in various hues. One side of the crystal is primarily blues/yellows/greens, while the opposite side primarily displays reds, violets, and purples. The fracture surface shows all colors, including brassy hues. There is a small area with a thin white coating that looks like calcite.
no photo
ccc-8 ($ 25.00)
Flambeau mine, Rocket Pocket, Ladysmith, Rusk County, Wisconsin, USA
CHALCOCITE specimen ccc-9
$ 60.00
Dims: 1.03x0.75x0.72" (2.62x1.92x1.82cm)
Wt: 0.49oz (13.9g)
Flambeau mine, Rocket Pocket, Ladysmith, Rusk County, Wisconsin, USA
This small chalcocite specimen displays a number of excellent pseudohexagonal crystals, some prismatic and others tabular. It is clearly a cluster of multiple distinct crystals, although most of them have distorted shapes. All of the chalcocite displays an irridescent blue color which transitions to a purple hue at some angles. There are a few places which appear silvery with a bright metallic luster, and a loupe reveals that these appear to be fresh fracture surfaces with no tarnish. I am certain that these were attachment points for additional crystals which have broken away.
no photo
ccc-9 ($ 60.00)
Flambeau mine, Rocket Pocket, Ladysmith, Rusk County, Wisconsin, USA


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