Tetrahedrite-(Cd)

Chemical formula: Cu₁+₆(Cu₁+₄Cd₂+₂)Sb₃+₄S₂-₁₃

Tetrahedrite-(Cd) is a rare mineral from the tetrahedrite group, a cadmium analog of tetrahedrite, found as small, metallic-lustered grains.

## Characteristics Tetrahedrite-(Cd) is a very rare sulfide mineral belonging to the broader tetrahedrite group. It was approved as a new mineral species by the IMA in 2019. It occurs as very small, anhedral (irregular) grains, usually not exceeding 100 micrometers in size. Its appearance is typical for ore minerals – it has a metallic luster and a steel-gray to black color. ## Physical Properties Due to the small size of the grains, most physical properties are difficult to measure precisely. The mineral is opaque, with a strong metallic luster. Hardness is estimated at approximately 3-4 on the Mohs scale, which is typical for minerals of the tetrahedrite group. The density calculated based on the chemical formula and unit cell parameters is 5.11 g/cm³. ## Colors and Varieties The mineral has a steel-gray to black color. In reflected light under a microscope, its color is gray. There are no distinct color varieties or commercial varieties. ## History and Name The name "Tetrahedrite-(Cd)" refers to its structural relationship with tetrahedrite and the dominance of cadmium (Cd) in a specific position within the crystal structure. It was discovered in the Zapadnoye uranium mine in the Krasnokamensk region (Zabaykalsky Krai, Russia). It was described by a team of mineralogists led by Igor V. Pekov and approved by the International Mineralogical Association (IMA) in 2019 (IMA 2019-051). ## Uses Tetrahedrite-(Cd) has no industrial application due to its extreme rarity and microscopic size. It is solely of scientific importance and is an object of interest for specialized collectors of rare minerals.

Properties

Mohs hardness: 3-4
Luster: Metallic
Streak: Black
Density: 5.11
Cleavage: None
Fracture: Uneven
Transparency: Opaque
Crystal system: Cubic

Diagnostic features

## Identification Identification of tetrahedrite-(Cd) is impossible without advanced laboratory techniques. It requires chemical analysis using an electron microprobe (EDS/WDS) to confirm the dominance of cadmium over zinc, iron, and other metals in the structure. Visually, it is indistinguishable from other minerals of the tetrahedrite group and many other sulfides. ## Distinguishing from Similar Minerals It can be confused with tetrahedrite-(Zn), tetrahedrite-(Fe), tennantite, sphalerite, galena, and many other gray, metallic sulfides. Definitive differentiation is possible only through chemical analysis. ## Crystal Forms It has only been observed in the form of irregular, anhedral grains intergrown with other minerals. No well-formed crystals have been observed.

Geological environment

## Genesis Tetrahedrite-(Cd) forms under hydrothermal conditions. At its type locality (Zapadnoye mine, Russia), it was found in calcite-fluorite veins cutting volcanic rocks (trachydacites). Its formation is associated with low-temperature hydrothermal processes that allowed for the concentration of cadmium. ## Mineral Associations At the type locality, it coexists with calcite, fluorite, as well as greenockite and hawleyite (other cadmium sulfides), indicating an environment rich in this element. It is also accompanied by other sulfides, such as pyrite or chalcopyrite. ## Localities The only confirmed and described locality for tetrahedrite-(Cd) in the world is the Zapadnoye (Западное) uranium mine near the city of Krasnokamensk, in Zabaykalsky Krai, Russia.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of a tetrahedrite-(Cd) specimen depends solely on the confirmation of its identity through chemical analysis. Since the mineral is microscopic, specimens do not possess aesthetic value in the traditional sense. The most valuable samples are those where tetrahedrite-(Cd) grains are relatively "large" (several tens of micrometers) and clearly visible in association with other minerals, and the specimen itself comes from the type locality and has analytical documentation. ## Popular Localities The only source of specimens is the type locality – the Zapadnoye mine in Russia. The availability of material is extremely limited, and it primarily goes to scientific institutions and highly specialized collectors of "microminerals" and rare species.

Care and storage

## Cleaning Specimens containing tetrahedrite-(Cd) are usually microscopic and occur within solid rock. They do not require and should not be cleaned mechanically or chemically. Any attempt at cleaning may damage the delicate mineral grains. ## What to Avoid Avoid all chemicals, ultrasonics, temperature changes, and abrasion of the specimen's surface. The mineral is potentially susceptible to oxidation in a humid environment. ## Storage Specimens should be stored under stable conditions, preferably in a closed display box, to protect them from dust, moisture, and mechanical damage. Due to their microscopic nature, specimens often require storage in special containers with descriptions and marked locations of the grains.

Sources

IMA Mineral List (CNMNC)