Tetrahedrite-(Ni)

Chemical formula: Cu₁+₆(Cu₁+₄Ni₂+₂)Sb₃+₄S₂-₁₃

Tetrahedrite-(Ni) is a very rare mineral from the tetrahedrite group, a copper, nickel, and antimony sulfosalt, distinguished by the presence of nickel in its structure.

## Characteristics Tetrahedrite-(Ni) is a sulfosalt belonging to the tetrahedrite group, in which nickel is the dominant element in one of the structural sites. It forms crystals with the typical tetrahedral shape for this group, although it often occurs as granular or massive aggregates. Its color is steel-gray to black, and on fresh fracture surfaces, it exhibits a strong, metallic luster. It is an opaque mineral. ## Physical Properties This mineral is characterized by a hardness ranging from 3 to 4.5 on the Mohs scale, making it relatively soft. Its density is significant, approximately 5.07 g/cm³. It does not exhibit cleavage, and its fracture is subconchoidal to uneven. It possesses a strong, metallic luster. ## Colors and Varieties The color of tetrahedrite-(Ni) is uniform, from steel-gray to black. The name "tetrahedrite-(Ni)" is not a commercial variety but a formal mineralogical name approved by the International Mineralogical Association (IMA), indicating the dominance of nickel. Other color or commercial varieties are not known for this specific mineral. ## History and Name The name "tetrahedrite" comes from the Greek word "tetraedron," referring to the common form of its crystals. The suffix "-(Ni)" was added to distinguish it from other members of the tetrahedrite group, in which other metals (such as iron, zinc, or silver) dominate. The mineral was formally described as a new species in 1984 based on specimens found in the Ayer Hitam tin mine in Selangor, Malaysia. ## Uses Due to its great rarity, tetrahedrite-(Ni) has no industrial applications. It is solely an object of scientific interest and a prized acquisition for advanced systematic mineral collections.

Properties

Mohs hardness: 3-4.5
Luster: Metallic
Streak: Black to brownish black
Density: 5.07
Cleavage: None
Fracture: Conchoidal to uneven
Transparency: Opaque
Crystal system: Isometric

Diagnostic features

## Identification Helpful identification features include: steel-gray to black color, strong metallic luster, relatively high density, and, if visible, the tetrahedral crystal habit. The streak is black to brownish-black. The mineral is not magnetic. ## Distinguishing from Similar Minerals Tetrahedrite-(Ni) is visually indistinguishable from other dark members of the tetrahedrite group, such as tetrahedrite-(Fe), tetrahedrite-(Zn), or tennantite. Definitive identification requires advanced chemical analyses, e.g., by EDS, to confirm the dominance of nickel. It is distinguished from galena by the absence of cleavage, and from sphalerite by a different crystal habit and streak color. ## Crystal Forms It most often forms well-developed crystals with a tetrahedral habit. It also occurs as disseminated grains and massive, compact aggregates.

Geological environment

## Genesis This is a hydrothermal mineral, crystallizing under low and medium temperature conditions. It forms in ore veins, where it precipitates from solutions rich in copper, antimony, sulfur, and nickel. ## Mineral Associations Tetrahedrite-(Ni) coexists with other sulfides and sulfosalts. In the type locality (Malaysia), it was found in association with cassiterite, stannite, chalcopyrite, arsenopyrite, and pyrite. In other places around the world, it is also accompanied by quartz, dolomite, and other vein minerals. ## Localities The most important and type locality is the Ayer Hitam mine in Selangor, Malaysia. Other confirmed occurrences include the Bytíz mine in the Czech Republic, marble quarries in Carrara, Italy, and the area around Zinkgruvan in Sweden. Despite these few localities, it is an extremely rare mineral.

Rarity

Very rare

For collectors

## Quality Criteria The most sought-after by collectors are specimens with sharp, well-formed tetrahedral crystals, free from damage. Crystals embedded in a contrasting matrix, such as white quartz or dolomite, are highly valued. Large crystal size and analytically confirmed provenance from a rare locality significantly increase the collectible value of the specimen. ## Popular Localities Specimens of collector significance mainly come from a few known localities, such as Bytíz in the Czech Republic or Carrara in Italy. However, even from these places, well-formed tetrahedrite-(Ni) crystals are rare and represent a valuable acquisition.

Care and storage

## Cleaning Specimens should be cleaned very carefully, preferably dry, using a soft brush to remove dust. If water is necessary, it should be distilled water, and the specimen should be thoroughly dried immediately to prevent oxidation and tarnishing of the surface. ## What to Avoid The mineral is sensitive to acids and other strong chemicals, which can damage it. It should be protected from scratching, as it is relatively soft. Prolonged exposure to moisture and air can lead to the formation of tarnish and loss of luster. ## Storage It is recommended to store specimens in a dry and stable environment, preferably in closed boxes or display cases. This will limit access to moisture and contaminants and protect delicate crystals from mechanical damage.

Sources

IMA Mineral List (CNMNC)