Roaldite
Chemical formula: (Fe,Ni)<sub>4</sub>N
A very rare iron-nickel nitride, found exclusively in iron meteorites as microscopic inclusions.
Properties
- Luster
- Metallic
- Density
- 7.23
- Transparency
- Opaque
- Crystal system
- Cubic
Diagnostic features
## Identification Identification of roaldite is impossible without specialized equipment. It requires the preparation of a polished section from a meteorite sample and observation under a reflected light metallographic microscope. Final confirmation is obtained by chemical analysis using an electron microprobe (EDS/WDS), which shows the presence of iron, nickel, and nitrogen. ## Distinguishing from Similar Minerals Under the microscope, roaldite can be confused with other rare metallic-luster meteoritic minerals, such as schreibersite ((Fe,Ni)₃P), cohenite ((Fe,Ni)₃C), or carlsbergite (CrN). Definitive differentiation is only possible based on chemical composition analysis, which allows for the detection of nitrogen and distinguishes it from phosphides (schreibersite) and carbides (cohenite). ## Crystal Forms Roaldite forms microscopic, oriented lamellae or acicular inclusions within kamacite (an iron variety) crystals. Its crystals often exhibit an arrangement consistent with the crystal structure of the surrounding metal.
Geological environment
## Genesis Roaldite forms under extremely reducing conditions, at high pressures and temperatures prevailing within large asteroids that were the parent bodies for iron meteorites. It crystallizes directly from the metallic phase (iron-nickel alloy) during very slow cooling, lasting millions of years. ## Mineral Associations This mineral occurs in close association with the main components of iron meteorites: kamacite (as the leading mineral) and taenite. It is often accompanied by other rare meteoritic minerals, such as schreibersite, cohenite, and carlsbergite. ## Localities Confirmed occurrences of roaldite are very few. Besides the type locality in the Jerslev meteorite (Denmark), it has also been identified in the famous Canyon Diablo meteorite (Arizona, USA) and the Youndegin meteorite (Western Australia).
Rarity
Extremely rare
For collectors
## Quality Criteria Roaldite as such is not an object of collector's trade in the form of isolated specimens. Its value is inextricably linked to the meteorite in which it occurs. For collectors specializing in meteorite minerals, the greatest value is represented by a fragment (most often a polished section) of a documented meteorite with analytically confirmed presence of roaldite. A clear structure and the presence of other rare associated minerals enhance its attractiveness. ## Popular Localities The most well-known and commercially available material in which roaldite can be found are fragments of the Canyon Diablo meteorite, originating from the famous Barringer Crater in Arizona.
Care and storage
## Cleaning Roaldite specimens are microscopic inclusions in iron meteorites and are not cleaned directly. Care applies to the entire meteorite specimen. Polished surfaces (sections) should only be wiped with a dry, soft microfiber cloth to remove fingerprints. ## What to Avoid The greatest threat to iron meteorites containing roaldite is moisture, which causes rapid corrosion (rusting). Contact with water, acids, chemicals, and sudden temperature changes should be strictly avoided. ## Storage Specimens should be stored in the lowest possible humidity, preferably in airtight containers (e.g., membrane boxes) or display cases with moisture-absorbing agents (e.g., silica gel). Prolonged exposure to air leads to specimen degradation.