Rathite-IV
Chemical formula: Pb₃As₅S₁₀
Rathite-IV is a rare lead arsenic sulfosalt, forming tiny, acicular crystals with a metallic luster.
Properties
- Mohs hardness
- 3
- Luster
- Metallic
- Streak
- Black
- Density
- 5.43
- Cleavage
- Perfect on {100}
- Fracture
- Uneven
- Transparency
- Opaque
- Crystal system
- Monoclinic
Diagnostic features
## Identification Identification of rathite-IV is based on its characteristic appearance – small, acicular or bladed crystals with a metallic luster and lead-gray color. The key factors are its occurrence location (Lengenbach quarry) and its association with other sulfosalts. ## Distinguishing from similar minerals It is practically impossible to distinguish it with the naked eye from other members of the rathite group (e.g., rathite, dufrénoysite) and other acicular lead sulfosalts. Certain identification requires advanced analytical methods, such as X-ray diffraction (XRD) or chemical analysis (EDS/WDS). ## Crystal forms Crystals are strongly elongated along the b-axis, forming acicular, hair-like, or bladed shapes. They often occur in tangled aggregates or as inclusions in other minerals, mainly in dolomitic marble.
Geological environment
## Genesis It is a hydrothermal mineral, formed as a result of metamorphism. It occurs in veins cutting through dolomitic marbles (skarns). It formed under relatively low-temperature conditions. ## Mineral associations It most commonly co-occurs with other lead and arsenic sulfosalts, such as sartorite, dufrénoysite, baumhauerite, jordanite, and liveingite. It is also accompanied by realgar, orpiment, pyrite, and dolomite. ## Localities The only confirmed and classic occurrence of rathite-IV in the world is the Lengenbach quarry in the Binn Valley (Binntal) in the canton of Valais, Switzerland. This is the type locality for this mineral.
Rarity
Very rare
For collectors
## Quality criteria The most prized specimens are those with well-formed, sharply terminated crystals, forming visually attractive groups on a light dolomitic matrix. The contrast of dark, metallic rathite-IV needles with white dolomite is desirable. Crystal size is a key factor, as most specimens are microscopic. ## Popular localities The only source of collector specimens is the historical locality in Lengenbach, Switzerland. This mineral is not commercially mined, and specimens on the market mainly come from old collections or sporadic finds.
Care and storage
## Cleaning Specimens should only be cleaned mechanically, using a soft brush to remove dust. Due to the presence of arsenic and lead, hands should be thoroughly washed after each contact with the mineral. Wet cleaning is not recommended. ## What to avoid Avoid contact with water, acids, and other chemicals that may react with sulfides. The mineral is brittle and susceptible to mechanical damage. It should not be heated, as this may lead to the release of toxic arsenic fumes. ## Storage Rathite-IV specimens should be stored under stable conditions, in sealed containers or display cases, to protect them from dust and physical damage. They should be kept away from moisture and direct sunlight.