Palladoarsenide
Chemical formula: Pd<sub>2</sub>As
Palladoarsenide is a rare palladium arsenide, forming small, metallic grains in association with other platinum-group minerals.
Properties
- Mohs hardness
- 5
- Luster
- Metallic
- Streak
- Black
- Density
- 10.39
- Cleavage
- Perfect on {001}
- Fracture
- Uneven
- Transparency
- Opaque
- Crystal system
- Monoclinic
Diagnostic features
## Identification Amateur identification of palladoarsenide is practically impossible due to its microscopic size and similarity to many other metallic sulfides and arsenides. Definitive identification requires advanced analytical methods, such as electron microprobe (EDS/WDS) or X-ray diffraction (XRD). In reflected light under a polarizing microscope, it exhibits strong anisotropy. ## Distinguishing from Similar Minerals It can be confused with other palladium arsenides (e.g., guanglinite, stillwaterite) or platinum-group minerals with a metallic luster. Differentiation relies solely on precise chemical composition and crystal structure analysis. ## Crystal Forms Palladoarsenide crystallizes in the monoclinic system. It forms very small, elongated, lamellar, or acicular crystals, typically less than 0.2 mm in size. It occurs as individual grains or inclusions within other minerals.
Geological environment
## Genesis Palladoarsenide is a hydrothermal mineral, crystallizing in the late stages of platinum-group metal deposit formation. It forms in serpentinite alteration zones and in magmatic deposits associated with ultramafic and mafic intrusions, where palladium and arsenic become concentrated in residual solutions. ## Mineral Associations It co-occurs with other platinum-group and noble metal minerals, such as palladseite (Pd₁₇Se₁₅), platarsite (PtAsS), sperrylite (PtAs₂), stillwaterite (Pd₈As₃), native gold (Au), as well as with chalcopyrite, pentlandite, pyrite, chromite, and minerals from the serpentine group. ## Localities The most important occurrences of this mineral are the type locality in Itabira (Minas Gerais, Brazil) and the Stillwater igneous complex (Montana, USA). It has also been found in nickel and copper deposits in the Norilsk region and on the Kola Peninsula in Russia, in the Bushveld Complex in South Africa, and in Sudbury, Canada.
Rarity
Very rare
For collectors
## Quality Criteria For a micromineral as rare as palladoarsenide, the primary criterion for value is the confirmed presence of the mineral on the rock matrix itself. The most highly prized specimens are those where the crystals, despite their microscopic size, are well-formed, visible, and identified. A rich association with other rare platinum-group minerals is also significant. ## Popular Localities From a collector's perspective, the most desirable specimens come from classic, well-documented localities, such as the Stillwater Complex in the USA or the Norilsk deposits in Russia, which have yielded the best-studied samples of this mineral.
Care and storage
## Cleaning Specimens containing palladoarsenide, typically microminerals, do not require cleaning. Any attempts at mechanical or chemical cleaning may damage the delicate crystals or their surroundings. If dust removal is necessary, a photographic air blower can be used to gently blow it off. ## What to Avoid Avoid contact with chemicals, especially acids, which can react with arsenides. Do not subject specimens to ultrasound or rapid temperature changes. Protect them from mechanical damage and scratching. ## Storage Micromineral specimens, such as palladoarsenide, are best stored in special, sealed "micromount" boxes, which protect them from dust, humidity, and mechanical damage. A label with precise locality information is crucial for scientific and collecting value.