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Cobaltite is an important ore of the element cobalt. It forms very interesting and unusual crystals rarely seen in the mineral kingdom, especially the icosahedral type. The name of Cobaltite, and its namesake cobalt, is derived from the German equivalent of the leprechaun or goblin, called "kobold". Legend has it that the metal cobalt was haunted by an underground "kobold", due to its failure to properly smelt like other metals.
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Chemical Formula |
CoAsS |
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Composition |
Cobalt sulfoarsenide, usually with some iron
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| Variable Formula |
(Co,Fe)AsS |
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Color |
Silver white to gray, sometimes with a pink or red tint from Erythrite coatings |
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Streak |
Dark gray to black |
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Hardness |
5.5 |
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Crystal System |
Orthorhombic |
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Crystal Forms
and Aggregates |
There is a debate regarding the exact crystal structure of Cobaltite. It visually and structurally fits into the isometric system, but x-ray spectroscope studies reveal a lack of full crystal symmetry, thereby classifying it in the orthorhombic system according to most sources.
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Transparency |
Opaque |
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Specific Gravity |
6.3 |
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Luster |
Metallic |
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Cleavage |
1,1 |
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Fracture |
Uneven |
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Tenacity |
Brittle |
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Complex Tests |
Becomes magnetic upon heating |
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In Group |
Sulfides; Simple Sulfides |
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Striking Features |
Crystal habits, lack of yellow color, and mode of occurrence. |
| Environment |
In mesothermal veins of sulfide deposits, and in hornfels. |
| Rock Type |
Sedimentary, Metamorphic |
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Popularity (1-4)
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3 |
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Prevalence (1-3)
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3 |
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Demand (1-3) |
2 |
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Cobaltite is mined for its cobalt content. Well-formed crystals, especially those from Sweden, are highly valued classics among collectors.
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Cobaltite is not a common mineral. Perhaps the best examples of this mineral come from Sweden. Sharp, interesting crystals of various different crystal habits have come from Tunaberg, Nyköping, Södermanland; and well formed, pyritohedral crystals were found at Västmanland, at Håkansboda and in the Pelle mine, Riddarhyttan. In Norway, crystals of Cobaltite were found in the Skuterud Mines, Modum, Buskerud.
Cobaltite is very rare in the U.S. Small complex crystals, as well as massive Cobaltite, came from the Kibblehouse Quarry, Perkiomenville, Montgomery Co., Pennsylvania; and Cobaltite with a coating of Erythrite has been found at the U.S. Mine, Gold Hill, Tooele Co., Utah.
In Canada, cubic crystals of Cobaltite come from the Brazil Lake occurrence, near Espanola, Sudbury District, Ontario; and large, massive and grainy masses come from the orefields at Cobalt, Timiskaming District, Ontario. |
Arsenopyrite - Forms in different crystal habits, slightly harder.Pyrite - Greater hardness, and usually has a yellowish color that is lacking in Cobaltite. Marcasite - Greater hardness, forms in different crystal habits.
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