Pillaite
Chemical formula: Pb²⁺₉Sb³⁺₁₀S²⁻₂₃ClO₀.₅
Pillait is a very rare, lead-gray sulfosalt mineral with chlorine, occurring as microscopic, acicular crystals.
Properties
- Mohs hardness
- 3-4
- Color
- Black
- Luster
- Metallic
- Streak
- Black to dark brown
- Density
- 0
- Cleavage
- None
- Fracture
- Irregular/Uneven
- Transparency
- Opaque
- Crystal system
- Monoclinic
Diagnostic features
## Identification Identification of pillait is possible almost exclusively using advanced laboratory methods, such as chemical analysis (EDS) and X-ray powder diffraction (XRD). Visually, in collecting conditions, it can be suspected based on its characteristic form (small, acicular, tangled crystals), metallic luster, and co-occurrence with other rare sulfosalts in a specific geological environment. ## Distinguishing from Similar Minerals Pillait is difficult to distinguish from other acicular lead-antimony sulfosalts, such as zinkenite, jamesonite, or boulangerite. Definitive differentiation requires chemical analysis to confirm the presence of chlorine, which is a key component of pillait. ## Crystal Forms Pillait forms very fine, elongated, acicular or hair-like crystals. They usually occur as haphazardly tangled aggregates (so-called "felt") or radial aggregates.
Geological environment
## Genesis Pillait forms as a result of low-temperature hydrothermal processes. It occurs in small calcite veins cutting barite-pyrite-iron deposits that have undergone metamorphism. Its formation is associated with the mobilization of lead, antimony, and sulfur in the presence of chloride-rich solutions. ## Mineral Associations This mineral co-occurs with other sulfosalts and sulfides. In its type locality (Buca della Vena), it was found in association with calcite, sphalerite, pyrite, barite, as well as rarer minerals such as moëloite, zinkenite, dadsonite, and boulangerite. ## Localities The only confirmed and thoroughly described occurrence of pillait in the world is its type locality: the Buca della Vena quarry, located in the Apuan Alps in Tuscany, Italy. This site is known for the occurrence of many rare and unique minerals.
Rarity
Very rare
For collectors
## Quality Criteria The quality of pillait specimens is primarily assessed based on the richness and abundance of its crystals on the rock matrix. The most valued samples are those with dense, well-formed, tangled aggregates of acicular crystals, clearly visible under a microscope. Contrast with the substrate mineral (most often white calcite) and the presence of other rare associated minerals are also important. ## Popular Localities The only source of pillait specimens is the Buca della Vena quarry in Italy. All samples available on the collector's market come from this single locality.
Care and storage
## Cleaning Pillait specimens, typically micromount minerals, should not be cleaned mechanically or chemically. Any contaminants, such as dust, should be removed only with a photographic blower brush or compressed air from a safe distance. ## What to Avoid Avoid contact with chemicals, acids, and washing in water, which could damage delicate crystals or associated minerals (e.g., calcite). Do not heat specimens or expose them to sudden temperature changes. ## Storage Micromount pillait specimens should be stored in specialized "micromount" boxes that protect them from dust, mechanical damage, and humidity. Avoid exposure to direct sunlight.