Tennantite-(Cd)
Chemical formula: Cu¹⁺₆(Cu¹⁺₄Cd²⁺₂)As³⁺₄S²⁻₁₃
Tennantite-(Cd) is a rare mineral from the tennantite group, an arsenosulfide of copper and cadmium, distinguished by the presence of cadmium as a key component.
Properties
- Mohs hardness
- 3.5-4
- Color
- Black
- Luster
- Metallic
- Streak
- Reddish-brown
- Density
- 4.724
- Cleavage
- None
- Fracture
- Conchoidal
- Transparency
- Opaque
- Crystal system
- Isometric
Diagnostic features
## Identification Identifying tennantite-(Cd) is extremely difficult and impossible without advanced analytical methods. Visually, it is indistinguishable from other black, metallic sulfides, especially from other minerals of the tennantite and tetrahedrite groups. Definitive identification requires chemical analysis (e.g., using an electron microprobe - EDS/WDS) to confirm the dominance of cadmium over zinc, iron, and other elements. ## Distinguishing from similar minerals It can be confused with tennantite-(Zn), tennantite-(Fe), tetrahedrite, enargite, or tenantite. All these minerals have a similar appearance (metallic luster, dark color) and often co-occur. The differences between them are based solely on chemical composition, which is not visually assessable. ## Crystal forms It most often occurs as anhedral (unformed) grains up to several hundred micrometers in size. Rarely, it forms small, subhedral crystals with a tetrahedral habit.
Geological environment
## Genesis Tennantite-(Cd) forms as a result of hydrothermal processes. In its type locality (Lengenbach), it is associated with dolomitic metamorphic rocks (marbles), where it crystallized under low-temperature conditions from solutions rich in sulfur, arsenic, copper, and cadmium. ## Mineral associations This mineral co-occurs with other sulfides and sulfosalts. In the Lengenbach quarry, it has been found in association with realgar, tennantite-(Zn), pyrite, sphalerite, and rare minerals such as hatchite and wallisite. ## Localities The only confirmed and described occurrence of tennantite-(Cd) in the world is the Lengenbach quarry in the Binn Valley (Binntal), Valais canton, Switzerland. This is its type locality.
Rarity
Extremely rare
For collectors
## Quality criteria As a microscopic mineral, tennantite-(Cd) is not evaluated according to typical criteria such as size or color. Its collector value is purely scientific and systematic. The most valuable specimens are those where the mineral has been unambiguously identified by chemical analysis and is visible in association with other rare minerals from this locality. ## Popular localities The only source of specimens is its type locality – the Lengenbach quarry in Switzerland. Research and collector material comes exclusively from there and is extremely difficult to acquire.
Care and storage
## Cleaning Specimens should be cleaned mechanically only, using a soft brush or paintbrush to remove dust. Due to its rarity and potential instability, contact with water and chemical agents should be avoided. ## What to avoid Avoid ultrasonic cleaners, all acids, detergents, and solvents. The mineral may be sensitive to rapid temperature changes and prolonged exposure to moisture, which can lead to its oxidation. ## Storage It is recommended to store it under stable conditions, in a dry environment, away from direct sunlight. It is best kept in a closed display box or cabinet to limit contact with air and dust.