A carved and polished cobaltite sphere, 1¾ inches in diameter. Photo courtesy of liveauctioneers.com and I.M. Chait Gallery/Auctioneers.
Cobaltite cabochons can have a lovely metallic luster. However, this gem material is very seldom faceted.
A carved and polished cobaltite sphere, 1¾ inches in diameter. Photo courtesy of liveauctioneers.com and I.M. Chait Gallery/Auctioneers.
Cobaltite cabochons can have a lovely metallic luster. However, this gem material is very seldom faceted.
| Data | Value |
|---|---|
| Name | Cobaltite |
| Formula | CoAsS |
| Colors | Silvery white to reddish, steel gray with a violet tinge; blackish gray. |
| Fracture | Uneven |
| Hardness | 5.5 |
| Cleavage | Perfect 1 direction |
| Crystallography | Orthorhombic. Crystals usually cubes and pyritohedra or combinations of forms; also massive; granular. |
| Birefringence | None |
| Luminescence | None |
| Luminescence Present | No |
| Absorption Spectrum | Not diagnostic |
| Pleochroism | None |
| Luster | Metallic |
| Specific Gravity | 6.33 |
| Transparency | Opaque |
| Etymology | From the composition. |
| Occurrence | High temperature deposits, in metamorphosed rocks, and in vein deposits. |
Cobaltite (silvery colored material) mixed with calcite (whitish-grayish material), 4.3 cm across at its widest. Photo by James St. John. Licensed under CC By 2.0.
Cobaltite is a rare sulfide mineral, used primarily as an ore for cobalt.
A tufa cast silver Navajo naja with three cobaltite cabs, with arrow hallmark for Kevin Yazzie (Dine, 20th century). Photo courtesy of liveauctioneers.com and Cowan’s Auctions. (Cropped to show detail).
With a hardness of 5.5 and perfect cleavage, cobaltites are suitable for jewelry with protective settings.
Although their metallic luster is their principal attraction, some specimens can also show a beautiful reddish color. Nevertheless, you’re more likely to find cobaltites in a mineral collection, if at all, than in a jewelry collection.
A faceted cobaltite would probably appeal most to a completist gem collector.
Faceters should note that cobaltite contains arsenic and cobalt. They should take precautions to prevent inhaling particles, protect their eyes, and wash their hands while cutting cobaltites.
Protective settings will help keep cobaltites from getting scratched, which can release small particles that can be accidentally ingested. However, normal jewelry wear should pose no further health risks.
With a specific gravity of 6.33, cobaltite is a dense material and will feel heavier for its size than most other gemstones. However, it’s actually less dense than other metallic gemstones of similar appearance: breithauptite (7.59-8.23); niccolite (7.78); and algodonite (8.38). All of these materials are also rarely faceted but occasionally cabbed.
Cobaltite has a grayish black streak. Please note that streak testing is a destructive test that should only be used on an unfinished piece as a last resort for identification.
Scientists have synthesized cobaltites for mineralogical research. However, there is no known jewelry use for this lab-created material.
There are no known gemstone enhancements for cobaltites.
Canada, notably the aptly named Cobalt, Ontario, and Sweden, notably Tunaberg, produce masses and fine crystals.
Other notable sources include the following:
This specimen from Tunaberg, Sweden features a cobaltite crystal, about 2 cm tall, on matrix, 6.2 x 3.7 x 3.5 cm. © Rob Lavinsky, www.iRocks.com. Used with permission.
Lapidaries could cut stones of any desired size from massive material.
Clean cobaltites with a soft brush, mild detergent, and warm water. For more care recommendations, consult our gemstone jewelry care guide.
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