Although covellite has attractive blue colors and shows iridescence, this rare mineral is difficult to cut. You can scratch it with a fingernail! As cut gems, they're strictly curiosities for collectors.
The International Gem Society (IGS) has a list of businesses offering gemstone appraisal services.
|Crystallography||Hexagonal. Crystals are tabular; also massive and cleavages.|
|Colors||Light to dark indigo blue; purplish; commonly iridescent, yellow and red.|
|Luster||Submetallic to resinous; opaque, except in thin slivers.|
|Fracture||Uneven. Brittle. Flexible in thin sheets.|
|Cleavage||Perfect and easy 1 direction.|
|Pleochroism||Strong, but visible only in very thin sheets.|
|Optics||o = 1.45, e = 2.629. Uniaxial (+).|
|Etymology||After Niccolo Covelli, the Italian chemist who discovered the mineral.|
|Occurrence||Secondary enrichment zones of copper mines.|
|Inclusions||Pyrite and chalcopyrite veins.|
Cut covellites (or covellines) have no great value. With hardness ranging from 1.5 to 2, coins and fingernails could scratch these gems. Although gem cutters have cut cabochons from this material, covellite would make a challenging jewelry stone.
Covellite’s iridescence, color, and brassy inclusions of pyrite and chalcopyrite also distinguish it visually from gems within its hardness range.
Covellite leaves a shining, gray-black streak. (Usually, metallic gems, like this copper sulfide, have a colored streak). You’ll likely have no occasion to conduct a destructive streak test for identification purposes. However, if you want to see firsthand one of the few gems to leave a non-white, non-colorless streak, use a small spare piece or test a piece on an inconspicuous spot.
Covellites have some unusual structural and electrical properties of interest to science and industry. This mineral is a naturally occurring superconductive material. Not surprisingly, researchers have synthesized it. Use of this synthetic material for jewelry or other adornment is unknown (and unlikely, given its softness).
The type locality for this gem is the infamous Mount Vesuvius. Italy, principally Sardinia, remains an important source of gem-quality material.
Other notable sources include:
- United States: Alaska; California; Colorado; Butte, Montana; South Dakota; Utah; Wyoming.
- Argentina; Australia; Bosnia-Herzegovina; Germany; New Zealand; Philippines; Serbia.
Gem cutters generally cut cabochons from massive or foliated material. As a result, the cabs can be very large, up to several inches long.
You’re more likely to find covellites, if at all, in mineral collections than in jewelry collections. Jewelry use isn’t recommended.
If you insist, consult our Gemstone Jewelry Cleaning Guide for care recommendations.