Qusongite
Chemical formula: W<sup>4+</sup>C<sup>4-</sup>
Qusongite is a natural tungsten carbide, an extremely rare mineral with a metallic luster, found mainly in chromium-rich rocks.
Properties
- Mohs hardness
- 9-10
- Luster
- Metallic
- Streak
- Gray
- Density
- 15.7
- Cleavage
- Imperfect on {1010}
- Fracture
- Uneven
- Transparency
- Opaque
- Crystal system
- Hexagonal
Diagnostic features
## Identification Identification of qusongite is impossible without advanced laboratory techniques. It requires analysis using a scanning electron microscope (SEM) with chemical composition analysis (EDS/WDS) or X-ray diffraction (XRD). In electron backscatter (BSE) images, it stands out with very high brightness due to its high tungsten content. It is a mineral with a metallic luster and a gray color. ## Differentiation from similar minerals Differentiation from other rare, metallic minerals occurring in similar environments (e.g., other platinum-group minerals, native tungsten, other carbides) is only possible based on chemical and structural analysis. ## Crystal forms Qusongite forms very small, anhedral (lacking well-formed faces) or rounded grains, typically ranging from 5 to 50 micrometers in size. It occurs as inclusions in other minerals, mainly chromite.
Geological environment
## Genesis Qusongite forms under extreme reducing conditions, with very low oxygen activity, in deep parts of the Earth's upper mantle. Its presence is associated with ultramafic rocks, such as dunites and harzburgites, which are part of ophiolite complexes. The mineral crystallizes directly from magma or as a result of metasomatic processes in an environment rich in carbon and metallic elements. ## Mineral associations This mineral co-occurs with other minerals typical of Earth's mantle rocks, such as chromite, forsterite (olivine), enstatite (pyroxene), as well as diamond, moissanite, graphite, and various metal alloys and carbides (e.g., titanium carbide - khamrabaevite). ## Localities The most important and type locality is the Luobusha ophiolite in Qusong County, Tibet (China). This is one of the world's richest sites for deep mantle minerals. Besides Tibet, its presence has also been reported in the Ray-Iz ophiolite in the Polar Urals, Russia.
Rarity
Extremely rare
For collectors
## Quality criteria The quality of a qusongite specimen is determined not by the appearance of the mineral itself (which is microscopic), but by the richness of the mineral association and confirmation of its presence by a reputable laboratory. The most valuable samples are host rock (chromitite or dunite) containing numerous, well-documented qusongite grains along with other rare minerals, such as diamond or moissanite. A specimen without an analytical certificate has no collector's value. ## Popular localities The only source of collectible specimens is the Luobusha ophiolite in Tibet. Specimens from this locality are highly prized by collectors specializing in systematic minerals and "micromounts."
Care and storage
## Cleaning Specimens containing qusongite, due to the microscopic size of the grains and their embedding in the host rock, generally do not require cleaning. Any attempts at mechanical or chemical cleaning may damage or remove the fine mineral grains. If dust removal is necessary, compressed air can be used from a safe distance. ## What to avoid Avoid contact with strong acids and chemicals. Despite its very high hardness, specimens are valuable due to their rarity, so avoid any abrasive actions that could damage the host rock and the qusongite grains themselves. ## Storage Specimens should be stored in stable conditions, away from dust and moisture, preferably in a sealed "micromount" box. A label with precise locality and identification is crucial, as qusongite grains are invisible to the naked eye.