Tashelgite
Chemical formula: CaMgFe²⁺Al₉O₁₆(OH)
Tashelgite is a very rare, blue-green mineral from the hibonite group, discovered near the Tashelga River in Russia.
Properties
- Mohs hardness
- 7.5
- Luster
- Vitreous
- Streak
- White
- Density
- 3.67
- Cleavage
- None
- Fracture
- Uneven
- Transparency
- Transparent,Translucent
- Crystal system
- Monoclinic
Diagnostic features
## Identification Identification of tashelgite is possible only through advanced laboratory methods, such as X-ray microanalysis (EDS/WDS) and X-ray diffraction (XRD), due to its microscopic size and occurrence as inclusions. Characteristic features include its specific chemical composition, blue-green color, and high hardness. ## Distinguishing from Similar Minerals It can be confused with other blue or green minerals from the hibonite or spinel group that occur in similar metamorphic environments. Definitive differentiation requires chemical analysis to confirm the unique combination of calcium, magnesium, iron, and aluminum in its structure. ## Crystal Forms Tashelgite forms small, tabular or platy crystals with a hexagonal outline, occurring as single grains or small clusters of inclusions in corundum.
Geological environment
## Genesis Tashelgite forms under conditions of high-grade contact metamorphism. It was found in rocks described as corundolites (corundum plagioclasites), which formed at the contact of gabbroid intrusions with dolomitic marbles. ## Mineral Associations This mineral co-occurs with corundum (in which it forms inclusions), spinelistrontianite, hibonite, hercynite, dmitryivanovite, and plagioclase. ## Localities The only confirmed locality of tashelgite in the world is its type locality – the corundum deposit near the Tashelga River in Gornaya Shoria, Kemerovo Oblast, Siberia (Russia).
Rarity
Extremely rare
For collectors
## Quality Criteria As a microscopic mineral, tashelgite is not evaluated according to typical criteria such as size or clarity. The collector's value of a specimen depends on the richness and distinctness of tashelgite inclusions in the host rock (corundum) and the quality of the rock specimen itself. The most valuable samples are those where tashelgite crystals are clearly visible under a microscope and unambiguously identified analytically. ## Popular Localities The only source of specimens is the type locality in Russia, which makes every specimen from this location extremely desirable for specialized collectors of rare minerals and micromounts.
Care and storage
## Cleaning Due to its extreme rarity and small crystal sizes, which occur as inclusions in the host rock, self-cleaning is not recommended. Specimens should be left in their untouched state. If dust removal is necessary, compressed air or a very soft brush can be used. ## What to Avoid Avoid contact with chemicals, acids, and strong detergents. Despite its high hardness, the specimen should be protected from impacts and abrasion, which could damage the much more delicate host rock. ## Storage Tashelgite specimens, as microscopic inclusions, should be stored in specialized "micromount" boxes, protecting them from dust and mechanical damage. Avoid exposure to extreme temperature changes.