Mineral
Chalcocite
Cu₂SKalkosin
A dark gray-black copper sulfide that is about 80 per cent copper by weight; for centuries one of the most profitable copper ores.
Also known as: Copper glance · Vitreous copper · Redruthite
- Popularly: Ore and raw material
- Ore
- Important in Türkiye
In short
Chalcocite is a mineral (Cu₂S) made of copper and sulfur, dark gray to black with a metallic lustre. About 80 per cent of its weight is copper, which makes it one of the richest sulfide ores of copper. It mostly forms in copper deposits, in the copper-enriched zone just below the air-weathered part. Its name comes from the Greek khalkos, meaning “copper”.
Photos
How does it form?
Most chalcocite forms in the copper-enriched zone just below the air-weathered part of a copper deposit: copper dissolved near the surface is carried down by water and is deposited lower down as chalcocite, replacing other copper minerals (supergene enrichment). That is why copper deposits can contain a zone of particularly high copper content. More rarely it also forms directly (as a primary mineral) in hot-water veins, and it can occur in sedimentary rocks. Minerals such as pyrite, chalcopyrite, covellite, bornite and molybdenite are found with it.
What is it used for?
Chalcocite has been mined for centuries and is one of the most profitable copper ores: its high copper content and the ease of separating copper from sulfur see to that. When concentrated by froth flotation, concentrates containing chalcocite can reach 70 per cent copper. According to MTA, chalcocite is also among the copper sulfide minerals best suited to leaching (separating copper from the ore with an acid solution). The copper obtained is used:
- in electrical and electronic equipment: cables, electric motors and circuit boards,
- in construction: water pipes and roofing,
- in alloys: brass (with zinc) and bronze (with tin).
The story of Kennecott
At Kennecott in Alaska, USA, mining began with the discovery of the green of malachite and of chalcocite found with it. According to Wikipedia, the first ore shipments contained 72 per cent copper; after the first shipment in 1911 the camp was abandoned in 1938 and is a ghost town today.
In Türkiye
At the Uslu copper mineralisation in Sivrice, Elazığ, MTA researchers identified chalcocite together with bornite, covellite, digenite and chalcopyrite. In the lead-zinc veins of İnler Yaylası (Şebinkarahisar) in Giresun, chalcocite is seen only rarely.
What determines its value?
Chalcocite is a good ore because of its high copper content (about 80 per cent of its weight) and because copper separates easily from its sulfur; even so, its worth depends on the size of the deposit, the copper content of the ore (its grade), the cost of mining and processing, and demand for copper. For collectors, well-formed, lustrous, undamaged crystals and specimens from famous localities such as Bristol (Connecticut), Cornwall or Flambeau (Wisconsin) are sought.
This information is educational, not buying, selling or investment advice. Value varies enormously with quality and treatment.
How to recognise it
- 1
Its colour is dark gray to black and its lustre metallic; its streak (powder colour) is blackish lead-gray.
- 2
It is soft (hardness 2.5–3): a steel knife scratches it easily. It is brittle and breaks with a shell-like curved surface (conchoidal).
- 3
It is very dense (specific gravity 5.5–5.8): it feels heavy for its size.
- 4
Crystals are short prisms or thick plates; twinning can build star-shaped groups that look hexagonal. It is mostly seen as masses or fine powdery coatings.
Fakes and imitations
What shops usually don’t tell you:
- Copper sulfides are hard to tell apart by eye: the colour of a fresh break (dark gray in chalcocite, copper-red in bornite, brass-yellow in chalcopyrite), hardness and streak give clues. For a certain identification, ask a specialist or a laboratory.
Safety
Chalcocite is a copper sulfide (about 80 per cent of its weight is copper). Handling it is generally harmless; wash your hands afterwards. Do not grind or sand it and breathe the dust: copper dust irritates the nose and throat and can cause dizziness and headaches. Do not put it in your mouth or lick it. Do not heat it; irritating sulfur dioxide gas is released. Do not put it in water to make “gem water” or an “elixir”: there is no knowing how much copper will dissolve, and too much copper causes nausea, vomiting, abdominal pain and diarrhoea, and with long exposure liver and kidney damage. Keep specimens away from children and pets.
Myths and misconceptions
MythChalcocite and chalcopyrite are the same mineral; their names are almost the same.
FactBoth are copper ores and both names come from the Greek khalkos (copper); but chalcocite is a copper sulfide (Cu₂S, dark gray-black, about 80 per cent copper) while chalcopyrite is a copper-iron sulfide (CuFeS₂, brass-yellow, about 35 per cent copper).
Did you know?
Chalcocite is also known as “copper glance”, “vitreous copper” and “redruthite”.
In ore concentrates containing chalcocite, the copper content can reach 70 per cent; in chalcopyrite concentrates it is about 15–30 per cent (MTA).
Besides being soft and brittle, it is somewhat sectile: a knife can cut it a little.
Where is it found?
Loading map…
- Bristol, Connecticut, USA · Known localityThe Handbook of Mineralogy names Bristol for exceptional chalcocite crystals (coordinate is the town centre)
- St. Just, Cornwall, England · Historic sourceThe Handbook of Mineralogy lists St. Just, St. Ives, Camborne and Redruth among the Cornish sources of fine chalcocite crystals (coordinate is the town of St. Just)
- Bisbee, Arizona, USA · Known localityA copper-mining town the Handbook of Mineralogy names for chalcocite (coordinate is the town centre)
- Butte, Montana, USA · Known localityA place the Handbook of Mineralogy names for chalcocite; the coordinate is the Berkeley Pit in the Butte mining district
- Kennecott, Alaska, USA · Historic sourceChalcocite was found together with malachite in the discovery that led to the mining camp; the first ore shipments are reported to have contained 72 per cent copper
- Flambeau mine, Ladysmith, Wisconsin, USA · Known localityThe Handbook of Mineralogy mentions chalcocite crystals from the Flambeau mine south-west of Ladysmith
- Telfer, Western Australia · Known localityA mine the Handbook of Mineralogy names for fine chalcocite crystals
- Uslu, Sivrice, Elazığ, Türkiye · Known localityBornite, chalcocite, covellite and digenite are reported from the Uslu copper mineralisation about 30 km south-west of Sivrice (coordinate is the Sivrice district centre)
- İnler Yaylası, Şebinkarahisar, Giresun, Türkiye · Known localityChalcocite and covellite are reported rarely in the lead-zinc veins (coordinate is the Şebinkarahisar district centre)
Locations are approximate to protect sites. Red dots mark places in Türkiye. Open in the big map →
Frequently asked questions
What is chalcocite?
Chalcocite is a mineral (Cu₂S) made of copper and sulfur, dark gray to black with a metallic lustre. About 80 per cent of its weight is copper, which makes it one of the richest sulfide ores of copper. It mostly forms in copper deposits, in the copper-enriched zone just below the air-weathered part. Its name comes from the Greek khalkos, meaning “copper”.
What is chalcocite used for?
Chalcocite has been mined for centuries and is one of the most profitable copper ores: its high copper content and the ease of separating copper from sulfur see to that. When concentrated by froth flotation, concentrates containing chalcocite can reach 70 per cent copper. According to MTA, chalcocite is also among the copper sulfide minerals best suited to leaching (separating copper from the ore with an acid solution).
How hard is chalcocite?
It has a hardness of 2.5–3 on the Mohs scale. A fingernail cannot scratch it, but a steel knife can. Its specific gravity is 5.5–5.8 g/cm³.
Where is chalcocite found?
Its best-known localities: St. Just, Cornwall, England; Kennecott, Alaska, USA; Bristol, Connecticut, USA; Bisbee, Arizona, USA; Butte, Montana, USA.
Where is chalcocite found in Türkiye?
Known localities in Türkiye: Uslu, Sivrice, Elazığ, Türkiye; İnler Yaylası, Şebinkarahisar, Giresun, Türkiye.
How can you tell if chalcocite is real?
Its colour is dark gray to black and its lustre metallic; its streak (powder colour) is blackish lead-gray. It is soft (hardness 2.5–3): a steel knife scratches it easily. It is brittle and breaks with a shell-like curved surface (conchoidal). It is very dense (specific gravity 5.5–5.8): it feels heavy for its size. Copper sulfides are hard to tell apart by eye: the colour of a fresh break (dark gray in chalcocite, copper-red in bornite, brass-yellow in chalcopyrite), hardness and streak give clues. For a certain identification, ask a specialist or a laboratory.
Is chalcocite valuable?
On the “street to diamond” value ladder it sits on step 4 of nine: Fine dimension stone and ore. Chalcocite is a good ore because of its high copper content (about 80 per cent of its weight) and because copper separates easily from its sulfur; even so, its worth depends on the size of the deposit, the copper content of the ore (its grade), the cost of mining and processing, and demand for copper. For collectors, well-formed, lustrous, undamaged crystals and specimens from famous localities such as Bristol (Connecticut), Cornwall or Flambeau (Wisconsin) are sought.
Is chalcocite dangerous?
Chalcocite is a copper sulfide (about 80 per cent of its weight is copper). Handling it is generally harmless; wash your hands afterwards. Do not grind or sand it and breathe the dust: copper dust irritates the nose and throat and can cause dizziness and headaches. Do not put it in your mouth or lick it. Do not heat it; irritating sulfur dioxide gas is released. Do not put it in water to make “gem water” or an “elixir”: there is no knowing how much copper will dissolve, and too much copper causes nausea, vomiting, abdominal pain and diarrhoea, and with long exposure liver and kidney damage. Keep specimens away from children and pets.
Sources
- Handbook of Mineralogy: Chalcocite · Mineralogical Society of America
- Chalcocite · Wikipedia
- Türkiye ve Dünyada Bakır · MTA Genel Müdürlüğü, Fizibilite Etütleri Dairesi Başkanlığı, 2021
- Copper (fact sheet: ToxFAQs) · Agency for Toxic Substances and Disease Registry (ATSDR), U.S. CDC
- Elazığ-Sivrice-Uslu Cu Cevherleşmesinin Jeolojik Özellikleri (A. Aydın, Ö. Dumanlılar, M. Yığmatepe) · 56. Türkiye Jeoloji Kurultayı bildiri özü (Maden Yatakları oturumu)
- İnler Yaylası (Şebinkarahisar-Giresun) Kurşun-Çinko Yataklarında Sıvı Kapanım ve Kararlı İzotoplar (O ve H) Jeokimyası İncelemeleri (A. Gökçe, G. Bozkaya) · 56. Türkiye Jeoloji Kurultayı bildiri özü (Maden Yatakları oturumu)
- Bristol, Connecticut · Wikipedia
- St Just in Penwith · Wikipedia
- Bisbee, Arizona · Wikipedia
- Berkeley Pit · Wikipedia
- Kennecott, Alaska · Wikipedia
- Flambeau Mine · Wikipedia
- Telfer mine · Wikipedia
- Sivrice · Wikipedia
- Şebinkarahisar · Wikipedia
External links
Draft: awaiting expert reviewReport an error ↗
On the same step
Anglesite
A heavy lead sulfate mineral with a diamond-like shine that grows as a crust around galena; it is named after the island of Anglesey in Wales.
Arsenopyrite
A widespread silvery-grey sulfide containing arsenic: it smells of garlic when struck and is poisonous.
Banded iron formation
An ancient rock of alternating iron-oxide and chert bands: the record of oxygen beginning to build up on Earth, and the main source of iron ore.