Cobaltpentlandite
Chemical formula: Co<sub>9</sub>S<sub>8</sub>
Cobaltopentlandite is a rare cobalt and iron sulfide, a cobalt analogue of pentlandite, occurring as fine, metallic grains.
Properties
- Mohs hardness
- 4.5-5
- Luster
- Metallic
- Streak
- Black
- Density
- 5.15
- Cleavage
- None
- Fracture
- Uneven
- Transparency
- Opaque
- Crystal system
- Cubic
Diagnostic features
## Identification Amateur identification of cobaltopentlandite is practically impossible due to its microscopic size and similarity to other sulfides. It requires advanced laboratory methods, such as chemical composition analysis (EDS) and examination under a reflected light ore microscope, where it exhibits a characteristic pinkish-brown color. ## Distinguishing from Similar Minerals It can be confused with pentlandite, chalcopyrite, pyrrhotite, or bornite, with which it often co-occurs. Differentiation is based on chemical analysis – cobaltopentlandite is distinguished by its high cobalt content. Pentlandite is usually lighter, with a more yellowish hue. ## Crystal Forms It most often forms fine, anhedral (irregularly shaped) grains and aggregates. Poorly formed crystals with cubic or octahedral habits, usually less than one millimeter in size, are rarely observed.
Geological environment
## Genesis Cobaltopentlandite is a mineral of magmatic origin, crystallizing from sulfide melts in ultramafic and mafic igneous rocks, such as norites, gabbros, peridotites, and dunites. It forms during magmatic segregation processes in the late stages of intrusion crystallization. ## Mineral Associations It most commonly co-occurs with other sulfides, such as pentlandite, chalcopyrite, pyrrhotite, cubanite, and millerite. It is also accompanied by magnetite and platinum-group minerals (PGM). ## Localities The most important localities worldwide, from which well-studied specimens originate, include the Norilsk region (Talnakh and Oktyabrskoye intrusions) in Siberia, Russia. It also occurs in the Bushveld Complex in South Africa, Sudbury in Canada, the Outokumpu region in Finland, and nickel deposits in Kambalda, Western Australia.
Rarity
Very rare
For collectors
## Quality Criteria The collector's appeal of cobaltopentlandite is very specific and primarily aimed at collectors specializing in systematic minerals or ore deposit minerals (so-called "micromounts"). Since this mineral rarely forms crystals visible to the naked eye, specimens where cobaltopentlandite grains are as large as possible and clearly contrast in color with the surrounding sulfide matrix are most valued. Scientific confirmation of the mineral's identification and precise locality of origin enhance its value.
Care and storage
## Cleaning Cobaltopentlandite specimens, due to their occurrence as fine grains within the host rock, usually do not require cleaning. If necessary, a soft brush can be used to remove dust. Avoid contact with water and chemical agents. ## What to Avoid The mineral is sensitive to moisture and oxygen, which can lead to its oxidation and color change. Avoid contact with acids and other chemicals. It should not be heated or exposed to sudden temperature changes. ## Storage It is recommended to store specimens in dry conditions, preferably in closed, airtight containers or display cases, to limit air and moisture access. Exposure should occur under stable environmental conditions.