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 ) 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 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 back in the 1970s, rocked the gemological world by producing some crystals which were both large and gemmy. Virtually every faceted stone over 1 carat (200 mg) in weight is from this single deposit, which has long been mined out. Most crystals were immediately snatched up by the major minerological museums of the world, further increasing the rarity of faceted gems.
The number of faceted gems over 2 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. However, it is still one of the rarest and most sought of collector's gems, with gems over a few carats virtually impossible to find.
- Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., Wiley, ISBN 0-471-80580-7
- Webmineral data