Erlichmanite
Chemical formula: Os<sup>2+</sup>(S<sub>2</sub>)<sup>2-</sup>
Erlichmanite is an extremely rare osmium sulfide, forming microscopic, metallic-lustered crystals with a cubic structure.
Properties
- Mohs hardness
- >5.5
- Luster
- Metallic
- Streak
- Black
- Density
- 8.25
- Cleavage
- None
- Fracture
- Uneven
- Transparency
- Opaque
- Crystal system
- Isometric
Diagnostic features
## Identification Identification of erlichmanite is impossible without advanced analytical techniques. Preliminary identification is based on finding black, metallic-lustered, cubic crystals in association with platinum group minerals in ultramafic rocks. Final confirmation requires chemical composition analysis (e.g., using electron microprobe - EDS/WDS) and structural analysis (X-ray diffraction - XRD). ## Distinguishing from Similar Minerals Erlichmanite can be confused with other opaque, metallic minerals with cubic crystallization, such as laurite (RuS₂), magnetite (Fe₃O₄), or chromite (FeCr₂O₄). Laurite is its routine analog, and differentiation is only possible by analytical methods. Magnetite is strongly magnetic, and chromite usually has a dark brown streak, in contrast to erlichmanite's black streak. ## Crystal Forms Erlichmanite crystallizes in the cubic system, most often forming well-developed, isometric crystals. The dominant forms are the octahedron {111} and the cube {100}, often occurring in combination.
Geological environment
## Genesis Erlichmanite is a mineral of magmatic origin. It forms in ultramafic igneous rocks, such as dunites and chromitites, where it crystallizes from residual, sulfur-rich, and platinum group element (PGE)-rich sulfide melts. It also occurs secondarily in placer deposits formed by the weathering and erosion of primary ultramafic rocks. ## Mineral Associations This mineral most often co-occurs with other platinum group minerals (PGM), such as laurite, osmiridium, iridosmine, native platinum, as well as chromite, magnetite, and various sulfides (e.g., chalcopyrite, pentlandite). ## Localities The most important erlichmanite localities worldwide include: - USA: Mac-Me-Creek, Trinity County, California (type locality). - Russia: Placer deposits in the Urals (Is River, Nizhny Tagil region) and in ultramafic massifs in Siberia (e.g., Kondyor). - Canada: Bushveld Complex in South Africa (though laurite is more common there), some nickel deposits in Sudbury, Ontario. - Colombia: In alluvial platinum deposits in the Chocó department.
Rarity
Very rare
For collectors
## Quality Criteria The collector's appeal of erlichmanite depends primarily on the size and development of the crystals. Most valued are specimens with sharp, well-defined crystals with a metallic luster, clearly standing out from the host rock. Due to the microscopic nature of the mineral, the quality of the specimen viewed under magnification is crucial. The presence of rare associated minerals, especially other platinum group elements, increases the value and attractiveness of the specimen. ## Popular Localities Specimens from the type locality in California (USA) and from the Russian Urals and Siberia, which yield some of the best-developed microcrystals, are considered classic and most sought after.
Care and storage
## Cleaning Erlichmanite specimens, due to their microscopic size and occurrence as inclusions, generally do not require and are not amenable to cleaning. Any attempts at mechanical or chemical cleaning of the host rock may damage or destroy the delicate crystals. ## What to Avoid Avoid contact with chemicals, especially strong acids. Do not subject specimens to ultrasound or sudden temperature changes. Despite its high hardness, the crystals are brittle and susceptible to mechanical damage. ## Storage Specimens containing erlichmanite are best stored under stable conditions, in sealed "micromount" boxes, which protect them from dust and mechanical damage. Avoid direct exposure to sunlight, although the mineral is stable to it.