Carlsbergite

Chemical formula: Cr³⁺N³⁻

Carlsbergite is an extremely rare chromium nitride, found mainly in iron meteorites, characterized by a metallic luster and tabular crystals.

## Characteristics Carlsbergite is a chromium nitride, occurring as very small, tabular or lamellar crystals, usually not exceeding several tens of micrometers in size. It most often forms inclusions within other minerals, primarily kamacite, within iron meteorites. It is opaque and has a gray color with a metallic luster. ## Physical Properties This mineral is characterized by high hardness, estimated at 6-7 on the Mohs scale. Its density, calculated based on unit cell parameters, is approximately 6.12 g/cm³. It has a metallic luster and a gray streak. ## History and Name Carlsbergite was first described in 1971 based on finds in iron meteorites from Cape York (Greenland), Sardis (Georgia, USA), and Agpalilik (Greenland). Its name honors the Carlsberg Foundation in Copenhagen (Denmark), which funded expeditions to collect Greenlandic meteorites. ## Uses Due to its extreme rarity and microscopic size, carlsbergite has no industrial applications. It is solely of scientific importance and is a subject of interest for specialized collectors of meteoritic minerals.

Properties

Mohs hardness: 7
Luster: Metallic
Streak: Gray
Density: 0
Cleavage: None
Fracture: Uneven
Transparency: Opaque
Crystal system: Isometric

Diagnostic features

## Identification Identification of carlsbergite is only possible using advanced laboratory techniques, such as ore microscopy (in reflected light) and chemical analysis using an electron microprobe (EDS/WDS). In reflected light, it is gray and isotropic. Under amateur conditions, it is impossible to identify. ## Distinguishing from Similar Minerals It can be confused with other microscopic, gray accessory minerals in meteorites, such as cohenite or schreibersite. Differentiation requires chemical composition analysis – carlsbergite is distinguished by the presence of chromium and nitrogen. ## Crystal Forms It forms very small, elongated, lath-like or tabular crystals, often with a hexagonal outline. It typically occurs as single, isolated grains or small aggregates within a metallic matrix.

Geological environment

## Genesis Carlsbergite crystallizes under strongly reducing conditions, with very low oxygen fugacity, which prevailed within the parent bodies from which iron meteorites originate. It forms as one of the late phases crystallizing from the metallic iron-nickel melt. ## Mineral Associations This mineral occurs almost exclusively in association with minerals typical of iron meteorites. Its most common associations are kamacite, taenite, cohenite, schreibersite, troilite, and daubréelite. ## Localities Its occurrence has been confirmed in numerous iron meteorites, including Cape York and Agpalilik (Greenland), Sardis and Social Circle (Georgia, USA), North Chile (Chile), Mundrabilla (Australia), and also in the Qingzhen enstatite chondrite (China).

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of a specimen with carlsbergite is practically identical to the quality of the meteorite itself in which it is found. For scientific and collecting purposes, the most valuable are polished sections (slabs) on which carlsbergite grains have been identified and marked. The size and clarity of these grains under the microscope increase the research value of the specimen. ## Popular Localities Specimens come from the fall sites of known iron meteorites, such as Cape York, Mundrabilla, or North Chile. However, this is not a mineral obtained in a typical way, and its presence is confirmed during laboratory analyses of fragments of these meteorites.

Care and storage

## Cleaning Specimens containing carlsbergite (usually in the form of polished meteorite sections) should be cleaned only with a dry, soft cloth or a soft-bristled brush to remove dust. Avoid all liquids and chemicals. ## What to Avoid Absolutely avoid contact with water, moisture, and chemicals, as these can cause corrosion of the surrounding metallic matrix (kamacite and taenite). Specimens should be protected from humid air, which can lead to rusting of the meteorite. ## Storage Meteorite specimens containing carlsbergite must be stored in very low humidity conditions. It is recommended to use sealed containers (e.g., membrane boxes) with a desiccant (silica gel). Storage in a dry, temperature-stable environment is crucial for specimen preservation.