Sartorite
Chemical formula: Pb<sup>2+</sup>As<sup>3+</sup><sub>2</sub>S<sup>2-</sup><sub>4</sub>
Sartorite is a rare lead arsenic sulfosalt, forming characteristic acicular crystals with a metallic luster, valued by collectors for classic specimens from the Lengenbach quarry in Switzerland.
Properties
- Mohs hardness
- 3
- Luster
- Metallic
- Streak
- Reddish-brown to chocolate-brown
- Density
- 5.05 - 5.11
- Cleavage
- Good on {010}
- Fracture
- Conchoidal to uneven
- Transparency
- Opaque
- Crystal system
- Monoclinic
Diagnostic features
## Identification Sartorite can be identified by its characteristic habit – it forms long, acicular or prismatic crystals, often with longitudinal striations. Key features also include its steel-gray color, metallic luster, and high density. The streak is reddish-brown to chocolate-brown. ## Distinguishing from similar minerals Sartorite is sometimes confused with other lead sulfosalts, such as boulangerite, jamesonite, or zinkenite, which form similar acicular aggregates. Differentiation often requires chemical or crystallographic analysis. However, knowledge of associated minerals and locality can be helpful – sartorite is strongly associated with dolomites from Lengenbach. Its reddish-brown streak distinguishes it from many similar minerals with a gray or black streak. ## Crystal forms Crystals are monoclinic but exhibit pseudo-orthorhombic symmetry. They most often take the form of elongated prisms, needles, or rods. They are often deeply grooved along the elongation axis. They occur as single crystals embedded in rock or as radial and tangled aggregates.
Geological environment
## Genesis Sartorite is a hydrothermal mineral. It forms in ore veins, most often in carbonate rocks, such as dolomites. Its formation is associated with low-temperature solutions rich in lead, arsenic, and sulfur. ## Mineral associations This mineral often co-occurs with other sulfosalts, especially baumhauerite, rathite, dufrenoysite, as well as realgar, orpiment, pyrite, and sphalerite. The host rock is usually dolomite. ## Localities The most important and classic locality for sartorite in the world is the Lengenbach quarry in the Binn Valley (Binnatal) in the canton of Valais, Switzerland. The best, exemplary specimens come from there. The mineral has also been found in small quantities in the USA (Washington, Nevada), Peru (Quiruvilca), and Italy (Val di Fassa).
Rarity
Rare
For collectors
## Quality criteria The most prized sartorite specimens are those with sharply terminated, well-formed, and undamaged crystals that exhibit a strong metallic luster. High value is placed on contrasting compositions where dark, acicular sartorite crystals are embedded in light, sugary dolomite. Crystal size and the richness of the aggregate also significantly increase the value of a specimen. ## Popular localities By far the most desirable and historically important locality is the Lengenbach quarry in Switzerland. Specimens from this location are considered the global standard for this mineral and fetch the highest prices on the collector's market.
Care and storage
## Cleaning Sartorite specimens should be cleaned very carefully, using a soft brush to remove dust. Distilled water may be used, but prolonged soaking should be avoided. After wet cleaning, the specimen must be thoroughly dried immediately. ## What to avoid Contact with acids and other chemicals that can damage the crystal surface should be strictly avoided. The mineral is soft and brittle, so it must be protected from impacts and scratches. Prolonged exposure to moisture can cause tarnish to form. ## Storage Collector specimens of sartorite are best stored in closed, padded boxes or display cases to protect them from dust, mechanical damage, and humidity fluctuations. Avoid storing in areas with high air humidity.