Tantalcarbide
Chemical formula: Ta<sup>4+</sup>C<sup>4-</sup>
Tantalkarbide is a very rare mineral from the carbide group, distinguished by its extremely high density and metallic luster.
Properties
- Mohs hardness
- 6-7
- Luster
- Metallic
- Streak
- Brownish
- Density
- 14.05
- Cleavage
- Imperfect on {100}
- Transparency
- Opaque
- Crystal system
- Cubic
Diagnostic features
## Identification The key diagnostic feature of tantalkarbide is its extremely high density, which can be estimated even with small grains. Other helpful features include hardness (6-7 on the Mohs scale), metallic luster, brownish streak, and occurrence in heavy mineral concentrates. However, definitive identification requires advanced analytical methods, such as X-ray microanalysis (EDS/WDS). ## Distinguishing from Similar Minerals Tantalkarbide is visually almost impossible to distinguish from niobocarbide (NbC), with which it forms a continuous solid solution – this requires chemical analysis. It can be confused with other dark, heavy minerals from alluvium, such as cassiterite, tantalite, or ilmenite. It is distinguished from cassiterite by its significantly higher density and hardness. Tantalite is usually less metallic and has a different crystal structure. ## Crystal Forms It most often occurs as rounded, abraded grains in alluvial deposits. Very rarely, it forms small, imperfectly developed crystals with a cubic habit.
Geological environment
## Genesis Tantalkarbide is a mineral of magmatic origin. Its primary deposits are not fully understood, but it is believed to crystallize in ultramafic alkaline rocks, such as carbonatites, or in kimberlites. It is mainly found in secondary deposits – alluvium and weathered sediments, where it accumulates due to its high density and resistance to weathering. It is also found as syngenetic inclusions in diamonds. ## Mineral Associations In alluvial deposits, it co-occurs with other heavy and resistant minerals, such as gold, platinoids, cassiterite, tantalite, ixiolite, zircon, and diamond. ## Locations The most important localities of this very rare mineral are in Russia, including the type locality in the alluvium of the Avdotinskaya River in Middle Timan (Komi Republic) and in the Ural region. It has also been reported in China (Sichuan province) and as inclusions in diamonds from various locations worldwide.
Rarity
Very rare
For collectors
## Quality Criteria Tantalkarbide specimens are valued primarily by collectors specializing in rare minerals and micromounts. The value of a specimen is determined primarily by the size of the grains – the larger, the more valuable. An additional advantage is the presence of even trace amounts of preserved crystal faces. The abundance of grains on a rock matrix or in a concentrate also increases the value. ## Popular Localities Specimens from Russian localities in the Urals and the Kola Peninsula, where historical finds originate, are considered classic and most desirable.
Care and storage
## Cleaning Specimens, due to their microscopic size, rarely require cleaning. If necessary, compressed air can be used to remove dust or the grains can be rinsed in distilled water or alcohol. Mechanical cleaning, which could remove small grains from the substrate, should be avoided. ## What to Avoid Tantalkarbide is a very chemically and physically stable mineral. It is resistant to most acids. However, strong abrasion, which could damage the surface of small grains, should be avoided. ## Storage Due to the small size of specimens, tantalkarbide is most often stored in special "micromount" boxes or in sealed vials to prevent their loss. Protect from dust.