Vaesite
Chemical formula: Ni<sup>2+</sup>(S<sub>2</sub>)<sup>2-</sup>
Vaesite is a rare nickel sulfide, most often forming small, metallic-lustered crystals of isometric habit, valued by collectors of systematic minerals.
Properties
- Mohs hardness
- 4.5-5.5
- Luster
- Metallic
- Streak
- Black with a greenish tinge
- Density
- 4.6-5.03
- Cleavage
- None
- Fracture
- Uneven to conchoidal
- Transparency
- Opaque
- Crystal system
- Isometric
Diagnostic features
## Identification Vaesite can be identified by its isometric, metallic-lustered crystals (cubes, octahedra), black color, relatively high density, and black streak with a greenish tint. The lack of cleavage is also a characteristic feature. ## Distinguishing from Similar Minerals Vaesite is difficult to distinguish from other minerals of the pyrite group without chemical analysis. It differs from pyrite (FeS₂) usually by a darker, more gray color (pyrite is brass-yellow) and slightly greater hardness. Distinguishing it from cattierite (CoS₂) and other similar sulfides (e.g., ullmannite) based on visual characteristics is often impossible and requires specialized tests (e.g., EDS). ## Crystal Forms Vaesite crystals are typical of the isometric system. Cubes, octahedra, and their combinations are most commonly found. Pentagonal dodecahedra (pyritohedra) also frequently occur. Crystals are usually small, rarely exceeding a few millimeters, and appear as single individuals or in small groups intergrown on the host rock.
Geological environment
## Genesis Vaesite is a mineral of hydrothermal origin. It forms at low and medium temperatures in ore veins, often in association with other nickel, cobalt, and iron sulfides. It can also form in sedimentary processes under reducing conditions, in sediments rich in organic matter. ## Mineral Associations This mineral co-occurs with other sulfides, such as pyrite, cattierite, polydymite, millerite, chalcopyrite, sphalerite, and galena. At its occurrence in Katanga, it is also accompanied by uranium minerals. ## Localities The most important and classic locality, from which the best specimens originate, is the Kasombo mine in Haut-Katanga Province in the Democratic Republic of Congo. Other known localities include Shinkolobwe (DRC), the Paradox Valley mine in Montrose County (Colorado, USA), the Müsen area in Germany, and some nickel deposits in Canada and Australia.
Rarity
Rare
For collectors
## Quality Criteria The most valued specimens by collectors are those with sharp, well-formed crystals with a strong metallic luster. Ideal crystals have the form of cubes or octahedra, without damage and with a minimal amount of gangue. Crystal size is very important – specimens with crystals larger than 5 mm are already considered exceptional. The aesthetic arrangement of crystals on the matrix also enhances their attractiveness. ## Popular Localities By far the most sought-after and highly valued vaesite specimens come from the type locality – the Kasombo mine in the Democratic Republic of Congo. Crystals from there are considered the global standard for this mineral.
Care and storage
## Cleaning Vaesite specimens should be cleaned very carefully. It is best to use a soft brush to remove dust. If necessary, compressed air can be used. Avoid washing in water, especially with detergents, as the mineral may undergo slow oxidation. ## What to Avoid Avoid contact with acids and other chemicals that may react with sulfides. The mineral is sensitive to humid environments, which accelerate weathering processes and can lead to the formation of secondary sulfate coatings (e.g., morenosite). It should not be heated or exposed to sudden temperature changes. ## Storage Collector's specimens of vaesite are best stored in a dry place, in closed, padded boxes or display cases, to limit access to moisture and air. Protect from dust and mechanical damage, as it is a brittle mineral.