Sinnerite
Chemical formula: Cu¹⁺₆As³⁺₄S²⁻₉
Sinnerite is a rare copper sulfarsenide, forming small, metallic-lustered crystals, found in hydrothermal deposits.
Properties
- Mohs hardness
- 4-4.5
- Color
- Bronze, steel-grey, silver
- Luster
- Metallic
- Streak
- grey-black
- Density
- 0
- Cleavage
- Perfect on {100}
- Fracture
- Uneven
- Transparency
- Opaque
- Crystal system
- Triclinic
Diagnostic features
## Identification Identifying sinnerite with the naked eye is practically impossible and requires laboratory analysis. Preliminary identification in a collection can be based on its characteristic form – small, acicular or platy crystals with a metallic luster, forming radial aggregates. Association with the locality (Lengenbach quarry) and co-occurring minerals is key. ## Distinguishing from similar minerals Sinnerite can be confused with other rare sulfosalts from Lengenbach, such as baumhauerite, rathite, or dufrénoysite. All form similar, small, grayish-black crystals with a metallic luster. Definitive distinction is only possible using analytical methods, such as X-ray diffraction (XRD) or chemical microanalysis (EDS/WDS). ## Crystal forms Sinnerite crystallizes in the triclinic system. It forms elongated, platy or acicular crystals, often exhibiting striations along the elongation axis. These crystals typically occur as radial or randomly tangled aggregates on a rock matrix, most often in dolomite vugs.
Geological environment
## Genesis Sinnerite is a mineral of hydrothermal origin. It forms from the crystallization of solutions rich in copper, arsenic, and sulfur, at relatively low temperatures. It occurs in veins and vugs cutting metamorphic rocks, such as dolomitic marbles. ## Mineral associations This mineral co-occurs with a rich assemblage of other sulfosalts, which is typical for its type locality. It is most often associated with: tennantite, sphalerite, jordanite, baumhauerite, rathite, dufrénoysite, as well as realgar, orpiment, and dolomite, which often forms the host rock. ## Localities The only confirmed and well-documented locality for sinnerite in the world is the Lengenbach quarry in the Binn Valley (Binntal), in the canton of Valais, Switzerland. This is the classic and type locality for this mineral.
Rarity
Very rare
For collectors
## Quality criteria The quality of sinnerite specimens is primarily judged by the abundance and development of the crystals. The most prized specimens are those with numerous, sharp, well-defined crystals forming aesthetically pleasing, radial aggregates. Contrast with the matrix (most often white dolomite) and the presence of rare associated minerals are also important. Due to the microscopic nature of the mineral, specimens are evaluated under magnification. ## Popular localities The only source of collector specimens is the Lengenbach quarry in Switzerland. Material from this locality is highly valued by collectors specializing in systematic minerals and so-called "micromounts."
Care and storage
## Cleaning Sinnerite specimens are extremely delicate due to the small size and fragility of the crystals. Cleaning should be kept to an absolute minimum. If necessary, compressed air (from a safe distance) can be used to remove dust. Avoid contact with water and any chemical agents. ## What to avoid Avoid ultrasonic cleaners, chemical agents (acids and bases), and sudden temperature changes. The mineral is susceptible to oxidation, so it should be protected from moisture. Do not touch fragile crystals with bare hands or any tools. ## Storage It is recommended to store sinnerite specimens in closed, airtight "micromount" containers, which protect them from dust, moisture, and mechanical damage. Display should be in stable conditions, away from direct sunlight and heat sources.