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Cuprite
Chemical Formula	Cu2O
Species	Oxides & Hydroxides
Crystal System	Isometric
Mohs Scale	3-4
Specific Gravity	6.14
Color	Dark red to conchineal red, sometimes almost black
Streak	Shining metallic brownish-red
Luster	Adamantine, Sub-Metallic, Earthy
Refractive Index	n = 2.849
Diaphaneity	Transparent, Translucent
Cleavage	Imperfect/FairInterrupted on , more rarely on .
Fracture	Conchoidal
Crystal Habit：Cubic, octahedral, and dodecahedral crystals; as hairlike capillary forms, earthy, compact granular and massive
Geological Setting：Found in the oxidised zones of copper deposits.

Its dark crystals with red internal reflections are in the isometric system hexoctahedral class, appearing as cubic, octahedral, or dodecahedral forms, or in combinations. Penetration twins frequently occur. In spite of its nice color it is rarely used for jewelry because of its low Mohs hardness of 3.5 to 4. It has a relatively high specific gravity of 6.1, imperfect cleavage and a brittle to conchoidal fracture. The luster is sub-metallic to brilliant adamantine. The "chalcotrichite" variety typically shows greatly elongated (parallel to [001]) capillary or needle like crystals forms.

It is a secondary mineral which forms in the oxidized zone of copper sulfide deposits. It frequently occurs in association with native copper, azurite, chrysocolla, malachite, tenorite and a variety of iron oxide minerals. It is known as ruby copper due to its distinctive red color.

Cuprite was first described in 1845 and the name derives from the Latin cuprum for its copper content.

Cuprite is found in the Ural Mountains, Altai Mountains, and Sardinia, and in more isolated locations in Cornwall, France, Arizona, Chile, Bolivia, and Namibia.

Cuprite as a gemstone

Though almost all crystals of cuprite are far too small to yield faceted gemstones, one unique deposit from Onganja, Southwest Africa, which was discovered in the 1970s, has produced crystals which were both large and gem quality. Virtually every faceted stone over one carat (200 mg) in weight is from this single deposit, which has long been mined out. The number of faceted gems over two carats (400 mg) is difficult to estimate, but according to Joel Arem, one-time curator for the Smithsonian National Gem and Mineral Collection in Washington DC, faceted cuprite of any size is considered one of the most collectible and spectacular gems in existence, with its deep garnet coloring and higher brilliance than a diamond. Only the gem's soft nature prevents it from being among the most valuable jewelry stones.