Tetrahedrite-(Zn)

Chemical formula: Cu₁+₆(Cu₁+₄Zn₂+₂)Sb₃+₄S₂-₁₃

Tetrahedrite-(Zn) is a zinc-dominant member of the tetrahedrite group, a sulfosalt mineral forming characteristic tetrahedral crystals with a metallic luster.

## Characteristics Tetrahedrite-(Zn) is a sulfosalt of copper, zinc, and antimony, belonging to the broad tetrahedrite group. Its name refers to the most common crystal form – tetrahedra (Latin: *tetraedrum*). It usually occurs as well-formed, individual crystals or their intergrowths. It is also found in granular aggregates and massive forms. It ranges in color from steel-gray to iron-black and is an opaque mineral. ## Physical Properties This mineral is characterized by a metallic luster, which can be dulled or matte on weathered surfaces. Its Mohs hardness is 3.5-4, meaning it is relatively soft and susceptible to scratching. The density ranges from 4.97-5.05 g/cm³, making it noticeably heavy for its volume. It exhibits no cleavage, and its fracture is conchoidal or uneven. ## Colors and Varieties The color of tetrahedrite-(Zn) is uniform, from steel-gray to black. As a mineral defined by the dominance of zinc, it is one of the members in the isomorphic series of the tetrahedrite group. Other members of this group include tetrahedrite-(Fe) with dominant iron, tetrahedrite-(Hg) with mercury, and freibergite, which is a silver-rich variety. Identification of a specific group member based on visual characteristics is impossible and requires chemical analysis. ## History and Name The name "tetrahedrite" was given in 1845 by Wilhelm Haidinger and comes from the Greek word *tetraedron* (tetrahedron), referring to the typical form of its crystals. The suffix "-(Zn)" was formally added in 2019 by the International Mineralogical Association (IMA) to precisely distinguish members of the tetrahedrite group based on the dominant element. ## Uses Tetrahedrite-(Zn), like other minerals in its group, can be a minor source of copper and antimony. If it contains silver, it is also exploited as an ore of silver. For collectors, it is primarily an interesting and classic mineral due to its attractive, well-formed crystals.

Properties

Mohs hardness: 3.5-4
Luster: Metallic
Streak: Black
Density: 4.97-5.05
Cleavage: None
Fracture: Subconchoidal to uneven
Transparency: Opaque
Crystal system: Cubic

Diagnostic features

## Identification The most important diagnostic feature of tetrahedrite-(Zn) is the form of its crystals – sharply pointed tetrahedra. Other important features include steel-gray or black color, strong metallic luster, lack of cleavage, and relatively low hardness. The streak of the mineral is black. ## Distinguishing from Similar Minerals Tetrahedrite-(Zn) can be confused with other members of its group, e.g., tennantite (the arsenic analogue), from which it requires chemical analysis to distinguish. It can also be confused with sphalerite, which, however, has excellent cleavage and a lighter streak. Galena, although also having a metallic luster, crystallizes in cubic forms and has excellent, three-directional cleavage. Bournonite forms different, often cyclic, twinned crystals.

Geological environment

## Genesis Tetrahedrite-(Zn) is a hydrothermal mineral. It forms in ore veins under low to medium temperature conditions. It is a typical component of many polymetallic deposits worldwide. ## Mineral Associations It often co-occurs with other sulfides and sulfosalts. Its most common associated minerals include chalcopyrite, pyrite, sphalerite, galena, bournonite, as well as gangue minerals such as quartz, calcite, dolomite, siderite, and barite. ## Localities Significant deposits and localities with well-formed tetrahedrite-(Zn) crystals are found in many places around the world. Classic localities include: Casapalca mine in Peru; Cavnic and Baia Sprie in Romania; Příbram in the Czech Republic. It also occurs in numerous mines in the United States (Colorado, Idaho, Utah) and in the Herodsfoot mine in Cornwall (England).

Rarity

Not very common

For collectors

## Quality Criteria The most highly valued by collectors are specimens with sharp, well-formed, and undamaged crystals with a mirror-like, metallic luster. Large crystal sizes (above a few centimeters) significantly increase the value. The attractiveness of a specimen is also enhanced by its placement on a contrasting matrix, for example, on white quartz or calcite, as well as associations with other rare or aesthetic minerals. ## Popular Localities Specimens from Romanian mines in the Maramureș region, especially from Cavnic, are considered the best for this mineral, yielding large, classic tetrahedra. Peruvian specimens from Casapalca, often in association with other sulfosalts, are also highly prized.

Care and storage

## Cleaning Tetrahedrite-(Zn) specimens should be cleaned very carefully. It is best to use a soft brush to remove dust. For heavier dirt, distilled water and a soft brush can be used. Ultrasonic cleaners should be avoided, as they can cause cracks. ## What to Avoid As a sulfide, tetrahedrite-(Zn) is sensitive to acids and some chemicals, which can cause etching or discoloration. Prolonged exposure to humid air can lead to the formation of a dull tarnish and loss of luster. Avoid sudden temperature changes. ## Storage Collector specimens of tetrahedrite-(Zn) are best stored in a dry and stable environment, for example, in sealed boxes or mineral display cases. This protects them from dust, moisture, and mechanical damage.

Sources

IMA Mineral List (CNMNC)