Magnesiocoulsonite

Chemical formula: MgV³⁺₂O₄

A black, metallic mineral from the spinel group, an oxide of magnesium and vanadium, found in marbles.

## Characteristics Magnesiocoulsonite is a rare mineral belonging to the spinel group. It forms small, black, isometric crystals, typically octahedral in habit, rarely exceeding 0.5 mm in size. It occurs as single, disseminated grains within the host rock. Its appearance is typical of many minerals from the spinel group – it is opaque and has a strong, metallic luster. ## Physical Properties This mineral is characterized by a hardness of approximately 6.5 on the Mohs scale, making it relatively resistant to scratching. It has a metallic luster and a black streak. It is a brittle mineral with an uneven, irregular fracture. It does not exhibit cleavage. ## Colors and Varieties Magnesiocoulsonite occurs exclusively in black. No colored or commercial varieties are known. ## History and Name The mineral's name refers to its chemical composition – the dominant magnesium (magnesio) and its relation to the vanadium spinel, coulsonite. It was approved as a new mineral by the International Mineralogical Association (IMA) in 1998. Its discovery was made in the Pereval marble quarry in Russia. ## Applications Due to its extreme rarity and microscopic crystal sizes, magnesiocoulsonite has no industrial applications. It is of purely scientific significance and is an object of interest for specialized collectors of rare minerals.

Properties

Mohs hardness
6.5
Luster
Metallic
Streak
Black
Density
0
Cleavage
None
Fracture
Irregular/Uneven
Transparency
Opaque
Crystal system
Isometric

Diagnostic features

## Identification Identification of magnesiocoulsonite requires advanced analytical methods, such as chemical composition analysis (EDS/WDS). Visually, it is almost impossible. In the host rock (marble), it appears as fine, black, metallic-lustrous grains with an octahedral shape. ## Distinguishing from Similar Minerals Magnesiocoulsonite is visually indistinguishable from other black spinels, such as magnetite, chromite, hercynite, or coulsonite itself. Definitive differentiation is possible only based on chemical analysis confirming the dominance of magnesium and vanadium. ## Crystal Forms It forms very small, well-formed isometric crystals, most often as octahedra. They occur as single, disseminated grains in the rock.

Geological environment

## Genesis Magnesiocoulsonite forms under conditions of high-grade metamorphism. Its typical environment is metamorphosed carbonate rocks – calcitic and dolomitic marbles that have been subjected to high temperatures and pressures. ## Mineral Associations This mineral coexists with other minerals typical of metamorphic rocks. In the type locality (Pereval quarry), it was found in association with calcite, dolomite, diopside, phlogopite, graphite, pyrite, pyrrhotite, tremolite, and other rare vanadium minerals, such as vanadium spinel and goldmanite. ## Localities The only confirmed and described locality of magnesiocoulsonite in the world is its discovery site – the Pereval marble quarry, near the town of Slyudyanka on Lake Baikal, in the Irkutsk Oblast, Russia.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of a magnesiocoulsonite specimen is assessed primarily based on the confirmation of its identity by analytical methods. The most valuable specimens are those with the largest possible (though still microscopic), sharply defined crystals, clearly visible against a contrasting host rock. The richness of the association with other rare minerals also increases the specimen's value. ## Popular Localities The only source of specimens is the type locality in Russia (Pereval quarry). Material from this location is extremely difficult to obtain and appears on the collector's market sporadically.

Care and storage

## Cleaning Specimens of magnesiocoulsonite, due to the microscopic size of the crystals and their embedding in the host rock, usually do not require cleaning. If necessary, compressed air can be used to remove dust. Avoid contact with water and chemical agents that could damage the host rock (marble). ## What to Avoid Avoid contact with acids, which react violently with marble. Do not subject the specimen to ultrasound or sudden temperature changes. Protect from strong impacts that could cause delicate crystals to chip. ## Storage Specimens should be stored under stable conditions, in a closed box or display case, to protect them from dust and mechanical damage. Due to the small size of the crystals, storage in "micromount" type boxes with appropriate labeling is recommended.

External references

Sources

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