Seligmannite
Chemical formula: Cu<sup>1+</sup>Pb<sup>2+</sup>As<sup>3+</sup>S<sup>2-</sup><sub>3</sub>
Seligmannite is a rare sulfosalt mineral, a lead-copper arsenosulfide with a metallic luster and characteristic, striated crystals.
Properties
- Mohs hardness
- 3
- Luster
- Metallic
- Streak
- Black with a reddish tint
- Density
- 5.3 - 5.4
- Cleavage
- Imperfect on {010} and {110}
- Fracture
- Uneven
- Transparency
- Opaque
- Crystal system
- Orthorhombic
Diagnostic features
## Identification Seligmannite can be identified by its lead-gray color, strong metallic luster, relatively high density, and characteristic, often striated, tabular crystals. Its streak is black with a reddish tint. ## Distinguishing from Similar Minerals Seligmannite is isostructural with bournonite (CuPbSbS₃) and often difficult to distinguish without advanced chemical analysis (EDS). Bournonite contains antimony instead of arsenic and is much more widespread. Visually, both minerals can be identical. It is distinguished from other sulfosalts by its specific crystal habit and paragenesis, especially in its type locality. ## Crystal Forms Crystals are typically small, with a tabular or short-prismatic habit. They often exhibit complex face development and characteristic striations parallel to the crystallographic axes. They occur as single crystals or small, intergrown groups.
Geological environment
## Genesis Seligmannite is a hydrothermal mineral. It forms at low to medium temperatures in ore deposits, most commonly in veins cutting through sedimentary rocks, such as dolomites. ## Mineral Associations This mineral often co-occurs with other sulfosalts and sulfides. In its type locality (Lengenbach), it is associated with numerous rare arsenic minerals, such as jordanite, dufrénoysite, baumhauerite, rathite, as well as pyrite, sphalerite, and tennantite. In other localities, it may occur with enargite, luzonite, tennantite, and pyrite. ## Localities The most important and classic locality for seligmannite, from which the world's best specimens originate, is the Lengenbach quarry in the Binn Valley (Binnatal) in Switzerland. It is also known from the Bingham Canyon mine in Utah (USA), Cerro de Pasco in Peru, and the Quiruvilca mine in Peru.
Rarity
Rare
For collectors
## Quality Criteria The most prized specimens by collectors are those with sharp, well-formed, undamaged crystals exhibiting a strong metallic luster. Aesthetically pleasing compositions where seligmannite crystals contrast with light dolomite or co-occur with other rare minerals from Lengenbach are also highly valued. Crystal size is a key factor – specimens with crystals exceeding a few millimeters are considered exceptional. ## Popular Localities By far the most sought-after and classic locality for this mineral is the Lengenbach quarry in Switzerland. Specimens from there are considered exemplary for the species. Specimens from Bingham Canyon in the USA, although also important, less frequently form such well-developed crystals as those from Switzerland.
Care and storage
## Cleaning Seligmannite specimens should be cleaned very carefully, using a soft brush to remove dust. Due to its fragility and potential reactivity, avoid washing it in water, and especially avoid using ultrasonics, which can damage delicate crystals. ## What to Avoid Avoid contact with chemicals, acids, and detergents. The mineral is sensitive to sudden temperature changes. Prolonged exposure to humid air can cause a dull patina to form on its surface. ## Storage Collectible seligmannite specimens are best stored in stable conditions, in closed display boxes or cabinets, to protect them from dust, humidity, and mechanical damage. Avoid placing heavier minerals on delicate seligmannite crystals.