Tennantite-(Zn)
Chemical formula: Cu¹⁺₆(Cu¹⁺₄Zn²⁺₂)As³⁺₄S²⁻₁₃
Tennantite-(Zn) is a rare copper-zinc arsenosulfide from the tennantite group, forming metallic-lustered, isometric crystals.
Properties
- Mohs hardness
- 3-4.5
- Luster
- Metallic
- Streak
- Black to reddish-grey
- Density
- 4.49
- Cleavage
- None
- Fracture
- Uneven to sub-conchoidal
- Transparency
- Opaque
- Crystal system
- Isometric
Diagnostic features
## Identification Identifying tennantite-(Zn) based on visual characteristics is very difficult. Key features include metallic luster, steel-gray to black color, and isometric crystals, often in the form of tetrahedra. However, definitive identification requires advanced analytical methods, such as X-ray microanalysis (EDS/WDS), to confirm the dominance of zinc over other divalent metals (e.g., iron, mercury) and arsenic over antimony. ## Distinguishing from Similar Minerals Tennantite-(Zn) is visually indistinguishable from other minerals of the tetrahedrite group, such as tennantite-(Fe), tetrahedrite-(Zn), or freibergite. All form very similar crystals and have comparable physical properties. Differentiation relies on precise determination of chemical composition. It is distinguished from sphalerite by its higher metallic luster and crystal habit. ## Crystal Forms Crystals are typically isometric, most often adopting the form of a tetrahedron, frequently with additional modifying faces of a cube or rhombic dodecahedron. It also occurs as granular aggregates and as inclusions in other minerals.
Geological environment
## Genesis Tennantite-(Zn) is a hydrothermal mineral. It forms in medium- and low-temperature ore veins. In its type locality (Lengenbach), it is associated with unique metamorphic and hydrothermal processes occurring within dolomites. ## Mineral Associations This mineral often co-occurs with other sulfosalts and sulfides. In the Lengenbach quarry, its typical associated minerals include sphalerite, tennantite, hatchite, wallisite, as well as realgar and orpiment. In other localities, it may occur with pyrite, chalcopyrite, and other minerals from the tetrahedrite group. ## Localities The most important and also the type locality for tennantite-(Zn) is the Lengenbach quarry in the Binn Valley (Binnental) in Switzerland. This is a world-renowned mineralogical site. Other confirmed occurrences are very few and include, among others, the Tsumeb mine in Namibia and several other localities in Europe where it has been analytically identified.
Rarity
Very rare
For collectors
## Quality Criteria Specimens with sharp, well-formed crystals and a strong, metallic luster are most valued by collectors. Ideal specimens are single, sharp tetrahedra or groups of crystals embedded in a contrasting rock matrix (e.g., white dolomite). Crystal size is a key factor – even small but well-formed crystals are sought after. Absence of damage and a natural, unoxidized luster significantly increase the value of a specimen. ## Popular Localities By far the most known and valued source of tennantite-(Zn) is its type locality: the Lengenbach quarry in Switzerland. Specimens from this location are considered classic and serve as a benchmark for this mineral.
Care and storage
## Cleaning Specimens should only be cleaned dry, using a soft brush or compressed air to remove dust. Contact with water, especially with detergents, is not recommended. ## What to Avoid Avoid contact with acids and other chemicals that may react with sulfides and arsenates. The mineral is susceptible to oxidation, so it should be protected from humid air, which can cause tarnishing. It should not be heated or exposed to sudden temperature changes. ## Storage It is recommended to store specimens in dry, stable conditions, preferably in sealed collector boxes or display cases with controlled humidity. This will limit oxidation processes and preserve the natural luster of the crystal surfaces.