Midnight blue covellite cabochon, 249 cts, 73.7 mm length, Leonard Mine, Butte, Montana. © 49erMinerals. Used with permission.
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.
| Data | Value |
|---|---|
| Name | Covellite |
| Colors | Light to dark indigo blue; purplish; commonly iridescent, yellow and red. |
| Hardness | 1.5 - 2 |
| Wearability | Display Only |
| Fracture | Uneven |
| Cleavage | Perfect and easy 1 direction |
| Formula | CuS |
| Etymology | After Niccolo Covelli, the Italian chemist who discovered the mineral. |
| Occurrence | Secondary enrichment zones of copper mines. |
| Inclusions | Pyrite and chalcopyrite veins. |
| Crystallography | Hexagonal. Crystals are tabular; also massive and cleavages. |
| Crystallographic Forms | |
| Refractive Index | 1.45-2.629 |
| Birefringence | 1.179 |
| Dispersion | Strong. |
| Luminescence | None |
| Luminescence Present | No |
| Pleochroism | Strong, but visible only in very thin sheets. Deep blue to pale blue. |
| Optics | o = 1.45, e = 2.629. Uniaxial (+). |
| Optic Sign | Uniaxial + |
| Luster | Submetallic to resinous. |
| Specific Gravity | 4.68 |
| Transparency | Opaque, except in thin slivers. |
| Phenomena | Iridescence. |
Covellite (latest Cretaceous to earliest Tertiary, 62-66 Ma; Leonard Mine, Butte, Montana, USA). Photo by James St. John. Licensed under CC By 2.0.
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.
Of course, just because a mineral doesn’t make good rough doesn’t mean it lacks beauty. Covellite’s colors and iridescence can also be appreciated in its natural crystal form, too.
In 2005, quartz stones with covellite inclusions appeared on the market. This so-called “Pink Fire” quartz can show a pink flash when viewed from different angles due to these inclusions.
“Pink Fire” quartz, very light brown with pink flash, 32.77 cts, oval buff cushion, Brazil. © The Gem Trader. Used with permission.
Covellite’s iridescence, color, and brassy inclusions of pyrite and chalcopyrite can help 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.
Iridescent violet and magenta covellite blades dusted with bright, brass-yellow chalcopyrite microcrystals. Covellite and chalcopyrite, Butte, Butte District, Silver Bow Co., Montana, USA. © Rob Lavinsky, www.iRocks.com. Used with permission.
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, but 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 the following:
Covellite, Calabona Mine, Alghero, Sassari Province, Sardinia, Italy. © Rob Lavinsky, www.iRocks.com. Used with permission.
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. Consult our Gemstone Jewelry Cleaning Guide for care recommendations.
Covellite, Reynolds Mine, Summitville Mine (Reynolds Tunnel; Golconda Tunnel), Summitville District (Summit District), Rio Grande Co., Colorado, USA. © Rob Lavinsky, www.iRocks.com. Used with permission.
IGS Become Member