Cuprite

Cuprite is a red mineral (Cu₂O) made of copper and oxygen. It forms octahedral or cube-shaped crystals ranging in colour from deep ruby or cochineal red to nearly black, and sometimes fine, hair-like needle crystals. It forms in the air-weathered upper part of copper deposits and is a minor ore of copper. Its name comes from the Latin cuprum, meaning “copper”.

Cuprite is a minor copper ore. In MTA’s table of the main copper minerals it has the highest copper content: 88.82 per cent (chalcocite 79.85, chalcopyrite 34.63). According to MTA, cuprite is not among the copper oxide minerals best suited to leaching (separating copper from the ore with an acid solution). Copper 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).

It has a hardness of 3.5–4 on the Mohs scale. A fingernail cannot scratch it, but a steel knife can. Its specific gravity is 6.14–6.15 g/cm³.

Its best-known localities: Nizhny Tagil, Ural Mountains, Russia; Dzhezkazgan (Jezkazgan), Kazakhstan; Rheinbreitbach, Germany; Tsumeb, Namibia; Kolwezi, Katanga, Democratic Republic of the Congo.

Its colour is cochineal red, ruby red or purplish red; thick crystals can look nearly black. Held to the light, thick parts look red and thinner parts yellow-orange. Its streak (powder colour) is shining brownish red. Its lustre ranges from adamantine to submetallic. Cinnabar (mercury sulfide), red glass and other red minerals can resemble cuprite. Cuprite’s hardness (3.5–4), specific gravity (6.1) and brownish-red streak help tell it apart: cinnabar’s streak is scarlet and its specific gravity is above 8.

On the “street to diamond” value ladder it sits on step 4 of nine: Fine dimension stone and ore. Cuprite is valued as an ore: about 89 per cent of its weight is copper, but it occurs in limited amounts in the oxidised near-surface parts of deposits, and its worth depends on the size of the deposit, the cost of mining and processing, and demand for copper. For collectors, deep red, transparent, well-formed, undamaged crystals and specimens from famous places such as Onganja and Tsumeb in Namibia or the Urals are sought. Because it is so soft, cut stones are rare and are meant more for collections than for jewellery.

Crystal-therapy writers regard cuprite as the “stone of survival”: they claim it helps with grounding and acceptance, and makes it easier to let go of needless stress and of the urge to control everything. According to the same sources, cuprite stimulates the root chakra and increases vitality. Some crystal sellers and crystal-therapy sites say cuprite helps against vertigo and altitude sickness. There is no scientific evidence that cuprite reduces stress, increases vitality or relieves vertigo and altitude sickness; for these symptoms see a doctor. Cuprite is copper(I) oxide and dissolves in acids: it should not be put in water, least of all an acidic drink, to make “gem water” or an “elixir”, and should not be put in the mouth; too much copper causes nausea, vomiting and, in time, liver and kidney damage. This section reports beliefs; it is not health information. There is no scientific evidence for these claims and no stone replaces medical treatment.

Cuprite is copper(I) oxide (about 89 per cent of its weight is copper). Handling it is generally harmless; wash your hands afterwards. Pure copper(I) oxide is reported to be harmful if swallowed or inhaled, to cause serious eye damage and to be very toxic to aquatic life; treat the mineral accordingly: do not grind or sand it, and do not breathe the dust or get it in your eyes. Do not put it in your mouth. It dissolves in acids, forming copper salts: do not put it in water, least of all acidic liquids such as lemon water or vinegar, to make “gem water” or an “elixir”. 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.