Orthogersdorffite
Chemical formula: Ni³⁺(AsS)³⁻
Orthogersdorffite is a rare nickel arsenosulfide, an orthorhombic polymorphic variety of gersdorffite, forming small, metallic grains.
Properties
- Luster
- Metallic
- Density
- 6.239
- Transparency
- Opaque
- Crystal system
- Orthorhombic
Diagnostic features
## Identification Identification of orthogersdorffite is impossible without advanced laboratory techniques. It requires analysis by X-ray diffraction (XRD) to confirm its orthorhombic crystal structure and chemical analysis (e.g., using an electron microprobe) to determine its composition. Preliminary identification in a polished section under a microscope relies on its optical properties in reflected light. ## Distinguishing from Similar Minerals The most difficult to distinguish is gersdorffite, which has an identical chemical composition but crystallizes in the isometric system. Differentiation is possible only by X-ray diffraction. Visually, it can be confused with many other metallic sulfides and arsenides, such as skutterudite, cobaltite, or ullmannite. Definitive differentiation requires chemical and structural analysis. ## Crystal Forms Orthogersdorffite most often forms microscopic, anhedral (xenomorphic) grains disseminated in the host rock or in other sulfides. Well-formed crystals are not observed.
Geological environment
## Genesis Orthogersdorffite is a mineral of hydrothermal origin. It forms in ore veins, typically under low to medium temperature conditions. Its presence is associated with mineralization processes where solutions rich in nickel, arsenic, and sulfur crystallize in rock fractures. ## Mineral Associations It co-occurs with other ore minerals. In the type locality (Littleham Bay, England), it was found in association with gersdorffite, ullmannite, nickeline, chalcopyrite, galena, sphalerite, quartz, and dolomite. In other localities, it may also be accompanied by cobaltite and other sulfoarsenides. ## Localities It is a very rare mineral, known from only a few localities worldwide. Besides the type locality in Littleham Bay, England, its occurrence has been confirmed, among others, in the nickel-chromium-cobalt mine near La Gallega in Spain; in the Schlema-Alberoda area in the Ore Mountains (Saxony, Germany); in mines in the Cobalt-Gowganda area in Ontario (Canada); and in silver mines near Kongsberg in Norway.
Rarity
Very rare
For collectors
## Quality Criteria The collector appeal of orthogersdorffite specimens is very specific and targeted at specialized collectors. Since this mineral is usually invisible to the naked eye, the value of a specimen lies not in its aesthetics, but in its rarity and scientific significance. The most valuable specimens are those from the type locality (Littleham Bay) or those whose presence has been analytically confirmed. Rich associations with other rare minerals also increase the value of such a specimen. ## Popular Localities The most sought-after and classic material for collectors is that originating from the type locality - Littleham Bay in Devon, England. Specimens from other confirmed localities, such as Schlema in Germany or Cobalt in Canada, are also highly valued by specialists.
Care and storage
## Cleaning Due to its microscopic size and occurrence as inclusions, specimens containing orthogersdorffite usually do not require and should not undergo mechanical cleaning. Any attempts at cleaning may damage both the mineral itself and the surrounding rock matrix. ## What to Avoid Avoid contact with acids and other aggressive chemicals that may react with sulfides. As an arsenic-containing mineral, it should not be heated, as this can lead to the release of toxic fumes. Hands should be washed after contact with the specimen. ## Storage Specimens with orthogersdorffite are best stored under stable conditions, in closed display boxes, to protect them from dust and mechanical damage. The label should include the exact location and information about the presence of this rare mineral.