Daubréelite
Chemical formula: Fe<sup>2+</sup>Cr<sup>3+</sup><sub>2</sub>S<sup>2-</sup><sub>4</sub>
Daubréelite is a rare, black, metallic iron-chromium sulfide, found almost exclusively in iron meteorites.
Properties
- Mohs hardness
- 3.5
- Luster
- Metallic
- Streak
- Black
- Density
- 3.81 - 4.02
- Cleavage
- Perfect on {111}
- Fracture
- Uneven
- Transparency
- Opaque
- Crystal system
- Cubic
Diagnostic features
## Identification Identification of daubréelite requires specialized methods. In polished meteorite samples (known as thin sections or polished mounts), it can be recognized under a reflected light microscope. It appears as dark gray, isotropic grains within brighter troilite or a metallic kamacite and taenite matrix. Definitive confirmation requires chemical analysis (e.g., electron microprobe) or X-ray diffraction. ## Distinguishing from Similar Minerals It can be confused with other opaque minerals in meteorites, such as chromite or graphite. Chromite is usually harder. Graphite is much softer and tends to smudge. In practice, without advanced equipment, distinguishing these minerals is impossible. ## Crystal Forms It most commonly occurs as irregular, rounded grains or lamellar aggregates. Rarely, it forms small, poorly developed octahedral crystals.
Geological environment
## Genesis Daubréelite is a high-temperature mineral, crystallizing under strongly reducing conditions, with very low oxygen and sulfur fugacity. Its formation is almost exclusively associated with iron meteorites (octahedrites, hexahedrites) and some chondrites (e.g., enstatite chondrites). It forms as one of the late sulfide crystallization products in the cooling parent body of an asteroid. ## Mineral Associations It most often co-occurs with troilite, forming characteristic lamellar intergrowths within it. It is also associated with kamacite, taenite, schreibersite, cohenite, and graphite. ## Localities As a meteoritic mineral, its localities are meteorite fall sites. It has been identified in many well-known iron meteorites, including Canyon Diablo (Arizona, USA), Toluca (Mexico), Coahuila (Mexico), and also in the Polish Morasko meteorite.
Rarity
Rare
For collectors
## Quality Criteria The collectible value of daubréelite is inextricably linked to the value of the meteorite in which it is found. For collectors specializing in meteorite minerals, attractive specimens (usually polished slices) are those in which daubréelite inclusions are relatively large, clearly visible, and form interesting textures with the surrounding troilite. Exceptionally rare, standalone crystals, though microscopic, are highly sought after by specialized research collections. ## Popular Localities The most famous and daubréelite-rich specimens come from classic iron meteorite localities such as Canyon Diablo (USA), Toluca (Mexico), and Mundrabilla (Australia).
Care and storage
## Cleaning Specimens containing daubréelite, due to their occurrence in a metallic meteorite matrix, are generally not cleaned. Any attempts at wet cleaning can lead to corrosion of the surrounding iron. If necessary, compressed air can be used to remove dust. ## What to Avoid Water, moisture, and chemical agents should be strictly avoided. Moisture is the main factor causing rusting in iron meteorites, leading to irreversible damage to the specimen, including daubréelite inclusions. ## Storage Specimens should be stored in an environment with the lowest possible humidity, preferably in sealed containers with a desiccant (e.g., silica gel). It is advisable to regularly check the condition of the specimen and replace the desiccant. Display should be in closed, dry display cases.