Coulsonite
Chemical formula: Fe²⁺V³⁺₂O₄
Coulsonite is a rare, opaque iron-vanadium oxide from the spinel group, found in magnetite deposits.
Properties
- Mohs hardness
- 4.5-5
- Luster
- Metallic
- Streak
- Dark brown to black
- Density
- 5.17
- Cleavage
- None
- Fracture
- Uneven
- Transparency
- Opaque
- Crystal system
- Isometric
Diagnostic features
## Identification Identifying coulsonite in the field is practically impossible due to its occurrence as small, intergrown grains, very similar to magnetite. Identification requires advanced laboratory methods, such as chemical composition analysis (EDS) and X-ray diffraction (XRD). In reflected light under a polarizing microscope, it differs from magnetite by its brighter, gray color. ## Distinguishing from Similar Minerals Coulsonite is most often confused with magnetite, in which it occurs. It is distinguished by the presence of vanadium in its chemical composition, a slightly different color in reflected light, and the lack of strong magnetic properties, although it can be found in magnetic ores. It can also be confused with other dark spinels, such as hercynite or chromite, from which it can only be distinguished by analytical methods. ## Crystal Forms Most often, it forms small, irregular or rounded grains less than a millimeter in size. Well-formed, small octahedral crystals, typical of minerals from the spinel group, are rarely observed.
Geological environment
## Genesis Coulsonite is a mineral of metamorphic or magmatic origin. It forms under high-temperature conditions in iron, titanium, and vanadium ore deposits. It typically crystallizes as a product of the mixing of vanadiferous magnetite during metamorphic processes. ## Mineral Associations It most commonly co-occurs with magnetite, in which it forms inclusions. It is also accompanied by ilmenite, hematite, rutile, as well as various minerals from the amphibole and pyroxene groups. ## Localities The most important localities worldwide include: - Type locality: Buena Vista mine in Churchill County, Nevada, USA. - Other known occurrences include the Bushveld Complex in South Africa, the Otanmäki gabbro complex in Finland, the Svierzhevskoye deposit in Russia, and some deposits in China and Australia.
Rarity
Very rare
For collectors
## Quality Criteria The quality of coulsonite specimens is difficult to assess in a traditional way, as it almost always occurs as microscopic inclusions in other minerals. For specialized collectors and scientific institutions, the most valuable samples are those with analytically confirmed high coulsonite content, originating from a well-documented locality. Visible under a microscope, well-formed microcrystals significantly increase the value of a specimen. ## Popular Localities Specimens from the type locality in Nevada (USA) and the Bushveld Complex (South Africa) are the most classic examples of this mineral in systematic collections.
Care and storage
## Cleaning Coulsonite specimens, usually intergrown in a rock matrix, can be cleaned with a soft, dry brush to remove dust. The use of water is not recommended unless the stability of associated minerals is confirmed. ## What to Avoid Avoid contact with strong acids and chemicals that could react with the mineral or host rock. Coulsonite is stable, but it should be protected from strong impacts due to its brittleness. ## Storage Store in a dry place, in separate display boxes, to avoid scratches from harder minerals. It does not require special protection from light or room temperature.