Yarlongite

Chemical formula: Cr₄Fe₄NiC₄

Yarlongite is a rare chromium, iron, and nickel carbide, found in ophiolitic rocks, characterized by a distinctive steel-gray color and metallic luster.

## Characteristics Yarlongite is a very rare mineral from the carbide group, composed of chromium, iron, nickel, and carbon. It occurs as small, hexagonal crystals or as grains embedded in the rock matrix. Typical specimens have a steel-gray color and a strong, metallic luster, giving them the appearance of fine metal filings. ## Physical Properties This mineral is characterized by a hardness ranging from 5.5-6 on the Mohs scale, making it relatively scratch-resistant. It is opaque and has a density of 7.19 g/cm³, which is a high value for a non-metallic mineral. It also exhibits perfect cleavage in one direction. ## Colors and Varieties Yarlongite is uniform in color and does not form varieties. Its only known color is steel-gray. ## History and Name The mineral's name comes from the Yarlung Tsangpo River, near which its type locality is situated in Tibet. It was officially recognized by the International Mineralogical Association (IMA) in 2007. It was discovered in the Luobusha ophiolite, a rock formation known for the occurrence of many rare and unusual minerals. ## Applications Due to its extreme rarity, Yarlongite 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: 5.5-6
Luster: Metallic
Streak: Black
Density: 7.19
Cleavage: {001}
Fracture: Conchoidal
Transparency: Opaque
Crystal system: Hexagonal

Diagnostic features

## Identification Identifying Yarlongite in the field is practically impossible without advanced equipment. In a collection, it can be recognized by its steel-gray color, metallic luster, and high density. Its black streak is also characteristic. However, final confirmation requires chemical and crystallographic analyses (e.g., XRD, EDS). ## Distinguishing from Similar Minerals Yarlongite can be confused with other metallic minerals of gray color, such as graphite, molybdenite, or some sulfides. However, it is distinguished by its significantly higher hardness (graphite and molybdenite are very soft) and specific chemical composition. Unlike magnetite, it does not exhibit magnetic properties. ## Crystal Forms This mineral forms small, tabular crystals with a hexagonal outline. Most often, it occurs as irregular grains or small aggregates within the parent rock.

Geological environment

## Genesis Yarlongite forms under specific geochemical conditions in ultramafic rocks, such as peridotites and chromitites, which are part of ophiolite complexes. Its genesis is associated with processes occurring deep within the Earth's mantle, and these minerals were brought to the surface during tectonic processes. ## Mineral Associations This mineral coexists with other rare minerals from the carbide group, alloys, and native elements, typical of the Luobusha ophiolite. These include, among others, chromite, cohenite, moissanite, diamond, native iron (kamacite), and other iron and chromium carbides. ## Localities The only confirmed and described occurrence of Yarlongite in the world is the Luobusha ophiolite in Tibet (China). This is its type locality.

Rarity

Extremely rare

For collectors

## Quality Criteria For collectors, the most important criterion is the confirmation of the mineral's authenticity through analysis. Since specimens are microscopic, their value depends on the size and quality of the Yarlongite grains and their relationship with the rock matrix. Well-formed, though still small, crystals are the most desired. ## Popular Localities The only source of Yarlongite specimens is the Luobusha ophiolite in Tibet. Material from this locality is extremely difficult to acquire and appears on the collector's market sporadically, usually offered by specialized dealers.

Care and storage

## Cleaning Specimens should only be dry-cleaned, using a soft brush or compressed air to remove dust. Contact with water and chemicals is not recommended. ## What to Avoid Avoid contact with water, acids, detergents, and all chemical agents. As a carbide, the mineral may be susceptible to oxidation and corrosion in a humid environment. It should be protected from extreme temperatures and moisture. ## Storage It is recommended to store specimens in dry, sealed containers, preferably with a moisture absorber (e.g., silica gel). Display should be in enclosed showcases, away from direct sunlight and sources of moisture.

External references

https://www.mindat.org/min-35899.html