THE MINERAL COBALTITE

Cobaltite although rare is still an important and valuable ore of cobalt, a strategically and industrially useful metal. The symmetry of cobaltite is somewhat in dispute. Its structure is very similar to the structure of pyrite, FeS2. The sulfur to sulfur link (S-S) in pyrite is replaced by an arsenic to sulfur link (As-S) in cobaltite. If the position of the arsenic is not ordered then the symmetry is the same as pyrite's symmetry which is in the isometric class, 2/m bar 3. However it appears from some x-ray spectroscopy studies that the arsenic is ordered there by breaking the higher symmetry and giving cobaltite a symmetry of the orthorhombic class, 2/m 2/m 2/m. But the debate is not settled yet.

Regardless of its actual symmetry, cobaltite forms isometric looking crystals. Either from really being isometric or from simply having such a similar structure to pyrite, cobaltite's crystals mimic those of pyrite. Although the crystal habits are similar to pyrite, cobaltite can not be confused with pyrite which is brassy yellow in contrast to cobaltite's silver gray or white color. Skutterudite on the other hand is also white and forms similar crystals although it has poor cleavage.

Often deposits of cobaltite will have a weathering crust of minerals such as erythrite, Co3(AsO4)2-8(H2O). Since cobalt is a strong coloring metal, minerals like erythrite are strongly colored, in this case a pink to bright purple. Miners called these colorful minerals "cobalt blooms" and used them as indicators of the presence of cobalt ores, such as cobaltite. Good crystals are usually common when cobaltite deposits are found and are a treasure for collectors.

PHYSICAL CHARACTERISTICS:

  • Color is white to silver gray.
  • Luster is metallic.
  • Transparency crystals are opaque.
  • Crystal System has been described as isometric; 2/m bar 3, but its actual structure is perhaps orthorhombic; m m 2 although the last word has not been said on this subject.
  • Crystal Habits include cubes, octahedrons, pyritohedrons and combinations of these isometric forms. If cobaltite is actually orthorhombic than these forms are either pseudocubes etc or they are pseudomorphs from a truly isometric phase which existed at higher temperature and/or pressure. Cobaltite is also commonly massive and granular.
  • Cleavage is distinct in three directions forming cubes.
  • Fracture is uneven to subconchoidal.
  • Hardness is 5.5
  • Specific Gravity is approximately 6.0 - 6.4+ (heavier than average for metallic minerals)
  • Streak is dark gray.
  • Other Characteristics: Striations on cube faces.
  • Associated Minerals are silver, chalcopyrite, pyrite, erythrite, skutterudite and other cobalt minerals.
  • Notable Occurrences include Cobalt, Ontario, Canada; Zaire; Siegerland, Germany; Skutterud, Norway; Tunaberg, Sweden; Sonora, Mexico; England; Boulder, Colorado and other USA localities.
  • Best Field Indicators are crystal habit, cleavage, color, streak, association with erythrite and luster.
COBALTITE specimens:
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COBALTITE specimen cob-1
$ 105.00
Dims: 2.4" x 1.7" x 1.5"(6.1 x 4.3 x 3.8 cm)
Wt: 4.29 oz.(121.7 g)
Riddarhyttan, Vastmanland, Sweden
Many Cobaltite crystals are embedded in the pyrrhotite matrix of this specimen. Though the Cobaltite's silvery-white color contrasts with the deep brown-gold of the matrix, the crystals are still difficult to see, as most of them are extremely small and there are many platelets of what appears to be biotite, whose pearly luster resembles the dull metallic luster of the tiny Cobaltites. One crystal, however, is very easy to see due to its size; it is much larger than any other visible crystal, with visible dimensions of 0.4 x 0.3"(1.0 x 0.8 cm). From the faces that can be seen, I am pretty certain that it possesses the pyritohedral crystal form that is quite common for this mineral. It is undamaged, though it is rough in form and marred by small, yellow metallic crystals embedded in it(likely pyrrhotite). Its Swedish locality is well-known, and it was collected there sometime between 1950 and 1960.
no photo
cob-1 ($105.00)
Riddarhyttan, Vastmanland, Sweden
COBALTITE specimen cob-2
$ 62.00
Dims: 1.8" x 1.8" x 1.3" (4.6 x 4.6 x 3.3 cm)
Wt: 4.09 oz. (115.9 g)
Pellegruvan, Riddarhyttan, Vastmanland, Sweden
This small hand specimen consists of at least 10 Cobaltite crystals that are partially embedded in a brown, muscovite-laden matrix rock. While none of these crystals show any human-induced damage, their forms are rather rounded for the most part, and several of the crystals are incomplete due either to growing conditions or to intergrowth with each other. The largest of these crystals has a diameter of 0.2" (5 mm), and though it is incomplete, it shows the best pyrithohedral form of the group. All have a bright, silvery color and a metallic luster and are, of course, opaque.
no photo
cob-2 ($ 62.00)
Pellegruvan, Riddarhyttan, Vastmanland, Sweden
COBALTITE specimen cob-3
$ 40.00
Dims: 1.1" x 1.0" x 0.6" (2.8 x 2.5 x 1.5 cm)
Wt: 25.4 g
Hakansboda, Sweden
This thumbnail specimen consists of a metallic host rock in which rest several Cobaltite crystals. These crystals show moderately good pyritohedral form, though they are warped and the largest one is slightly damaged. It measures 0.4" (1.0 cm) in diameter, whereas the other crystals average 0.1" (3 mm) in diameter. It would seem, however, that most of the matrix that contains these crystals is made up of either more Cobaltite or a similar sulfide mineral, as it also has a bright silvery coloration and a metallic luster. There are also a few tiny patches of a metallic mineral that has a deep golden coloration- I do not know what it is, though it is likely related to the Cobaltite.
no photo
cob-3 ($ 40.00)
Hakansboda, Sweden
COBALTITE specimen cob-4
$ 150.00
Dims: 1.2 x 1.1 x 0.7" (3.0 x 2.8 x 1.8 cm)
Wt: 1.2 oz. (34.6 g)
Pellegruevan, Riddarhyttan, Vaestmanland, Sweden
This small specimen consists of several pyritohedral Cobaltite crystals that are embedded in a matrix that itself appears to be made of a metallic mineral. One crystal in particular is exposed, and it appears to be the only one that shows any damage, which is minor. It measures 0.2" (5 mm) in diameter and shows excellent form, with well-defined edges and clean faces that possess a bright metallic luster. It has the standard silvery-white color of Cobaltite, and somehow I get the feeling that the matrix itself is made up either of more, massive Cobaltite, or a closely-related metallic sulfide.
no photo
cob-4 ($150.00)
Pellegruevan, Riddarhyttan, Vaestmanland, Sweden
COBALTITE specimen cob-5
$ 41.00
Dims: 1.7 x 1.6 x 1.4" (4.3 x 4.1 x 3.6 cm)
Wt: 3.50 oz. (99.4 g)
Elizabeth Lake, Espanola, Ontario, Canada
Several warped Cobaltite cubes are embedded in what appears to be a feldspar matrix in this specimen (actually, the matrix reminds me of labradorite, but lacks the color). Approximately half of them are damaged and possibly incomplete, though most are almost completely obscured by the matrix. Only one has good cubic form, with well-defined edges and clean faces, and it has visible dimensions of 0.2 x 0.2 x 0.1" (0.5 x 0.5 x 0.4 cm). All have the silvery-white color and metallic luster that are standard for this mineral, but their luster is slightly dull and many show a colorful iridescence that denotes a slight oxide or decomposition coating. There are likely more crystals trapped in this matrix, and one could easily expose more of those
no photo
cob-5 ($ 41.00)
Elizabeth Lake, Espanola, Ontario, Canada
COBALTITE specimen cob-6
$ 30.00
Dims: 1.2 x 1.0 x 0.7" (3.0 x 2.5 x 1.7 cm)
Wt: 17 g w/ base
Hakansboda Mine, Vastmanland, Sweden
This thumbnail specimen consists of a single Cobaltite crystal that is partly embedded in a metallic sulfide base. This crystal measures about 0.2" (5 mm) in diameter and is in good condition, showing little fresh damage. Its pyritohedral form is somewhat warped but still reasonably good, and it has the standard bright silvery-gray color and bright metallic luster of its specie. The piece is hot-glued onto a flat, acrylic base.
no photo
cob-6 ($ 30.00)
Hakansboda Mine, Vastmanland, Sweden
COBALTITE specimen cob-7
$ 50.00
Dims: 0.65x0.62x0.56" (1.65x1.56x1.42cm)
Wt: 0.17oz (4.7g)
Elizabeth Lake, Espanola, Ontario, Canada
This specimen displays several intergrown cubic crystals of cobaltite in a matrix that appears to be a plagioclase feldspar. The largest of the cobaltite crystals is retangular rather than a cube, and is missing one corner but it appears to be a growth pattern showing striations, and not damage. The other crystals are progressively smaller cubes. All have a bright silvery metallic appearance, somewhat reminiscent of galena. There is a network of fine cracks in the largest crystal, which is missing a tiny bit of one corner (damage). The next smaller crystal is missing quite a bit of one corner, exposing the uneven fracture of cobaltite.
no photo
cob-7 ($ 50.00)
Elizabeth Lake, Espanola, Ontario, Canada
 

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