Quatrandorite
Chemical formula: Ag<sup>1+</sup>Pb<sup>2+</sup>Sb<sup>3+</sup><sub>3</sub>S<sup>2-</sup><sub>6</sub>
Quatrandorite is a rare sulfosalt mineral, lead-gray to black, forming small, tabular crystals.
Properties
- Mohs hardness
- 3.5
- Luster
- Metallic
- Streak
- Black
- Density
- 5.34
- Cleavage
- Good on {010}
- Fracture
- Uneven
- Transparency
- Opaque
- Crystal system
- Tetragonal
Diagnostic features
## Identification Field identification of quatrandorite is practically impossible without advanced research methods. In a collection, it can be suspected based on its lead-gray color, metallic luster, specific crystal habit (if visible), and co-occurrence with other sulfosalts in hydrothermal veins. Definitive identification requires chemical analysis (EDS) and X-ray diffraction (XRD). ## Distinguishing from Similar Minerals Quatrandorite is visually indistinguishable from other minerals in the andorite group (senandorite), as well as from many other sulfosalts, such as zinkenite, jamesonite, or boulangerite. All these minerals have similar color, luster, and mode of occurrence. Differentiation relies solely on analysis of crystal structure and precise chemical composition. ## Crystal Forms It forms small, tabular or short-prismatic crystals, often elongated and striated along the vertical axis. Crystals rarely occur individually, usually forming fan-shaped, radial, or massive, granular aggregates.
Geological environment
## Genesis Quatrandorite is a hydrothermal mineral. It forms in medium- to low-temperature ore veins rich in silver, lead, antimony, and sulfur. It is one of the later crystallization products in complex sulfosalt parageneses. ## Mineral Associations It most commonly co-occurs with other minerals from the andorite group (senandorite), as well as with pyrite, sphalerite, galena, stibnite, tetrahedrite, jamesonite, boulangerite, quartz, and calcite. ## Localities The most important and classic localities for minerals of the andorite group, including quatrandorite, are mines in the vicinity of Baia Sprie and Herja in Romania. It is also known from the San José mine in Oruro, Bolivia, and several other localities worldwide where complex, polymetallic hydrothermal deposits occur.
Rarity
Rare
For collectors
## Quality Criteria The most desirable specimens for collectors are those with well-formed, sharp crystals with a distinct luster. Crystal groups forming aesthetic, radial or fan-shaped aggregates are particularly valuable. Contrast with a light matrix mineral, such as quartz, significantly enhances the specimen's appeal. Crystal size is a key factor – specimens with crystals exceeding a few millimeters are already considered exceptional. ## Popular Localities Classic and most prized specimens come from historical mines in Romania (Baia Sprie, Herja) and Bolivia (Oruro). Specimens from these localities are considered type examples for this species.
Care and storage
## Cleaning Specimens should be cleaned very carefully, using a soft brush to remove dust. Due to possible reactivity, contact with water and any chemical agents should be avoided. If it is necessary to remove loose contaminants, compressed air can be used from a safe distance. ## What to Avoid Ultrasonic cleaners, which can damage brittle crystals, should be avoided. The mineral is sensitive to acids and other chemicals. Prolonged exposure to humid air can lead to the formation of tarnish and slow oxidation. ## Storage Quatrandorite specimens should be stored in a dry place, preferably in closed display boxes, to protect them from dust, humidity, and mechanical damage. Direct contact with other minerals should be avoided to prevent scratching.