Skinnerite

Chemical formula: Cu₁+₃Sb₃+S₂-₃

Skinnerite is a rare copper-antimony sulfosalt with a metallic luster, found in low-temperature hydrothermal veins.

## Characteristics Skinnerite is a copper-antimony sulfosalt, belonging to rare minerals. It most often forms small, anhedral (irregularly shaped) grains and aggregates intergrown with other sulfide minerals. It is rarely observed in the form of small, prismatic crystals. It is characterized by a metallic luster and a steel-gray to iron-black color. On weathered surfaces, it may be covered with a bluish or iridescent tarnish, which is helpful in its identification. ## Physical Properties This mineral is relatively soft, with a Mohs hardness of 3. It is opaque and quite heavy, with a density of 5.26 g/cm³. It has a conchoidal fracture and a black streak. It does not exhibit cleavage. ## Colors and Varieties Skinnerite's typical color is steel-gray, transitioning to iron-black. No color or commercial varieties are distinguished. ## History and Name The mineral was approved as a new species in 1973. Its name honors Brian J. Skinner (1928-2019), an American mineralogist and geochemist from Yale University and the United States Geological Survey (USGS), for his contributions to sulfosalt research. ## Uses Skinnerite has no industrial application. It is solely an object of scientific and collecting interest.

Properties

Mohs hardness: 3
Luster: Metallic
Streak: Black
Density: 5.26
Cleavage: None
Fracture: Conchoidal
Transparency: Opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Identifying skinnerite under amateur conditions is very difficult. It can be preliminarily recognized by its metallic luster, steel-gray color, black streak, and high density. It often occurs in paragenesis with other copper and antimony sulfosalts. Definitive identification requires advanced research methods, such as X-ray diffraction (XRD) or chemical microanalysis (EDS). ## Distinguishing from Similar Minerals Skinnerite is visually almost indistinguishable from many other sulfosalts, such as tetrahedrite, tennantite, or wittichenite, with which it often co-occurs. Tetrahedrite crystallizes in the isometric system, and wittichenite in the orthorhombic system, but these features are not visible in granular aggregates. A helpful, though not unambiguous, clue can be the bluish tarnish on the surface of skinnerite. ## Crystal Forms Well-formed crystals are extremely rare and appear as small, columnar or prismatic forms. Skinnerite typically forms anhedral grains, granular aggregates, or intergrowths with other ore minerals.

Geological environment

## Genesis Skinnerite is a mineral of hydrothermal origin. It forms under low-temperature conditions in ore veins rich in copper and antimony. ## Mineral Associations It most commonly co-occurs with other sulfosalts and sulfides, such as wittichenite, tetrahedrite, tennantite, bornite, chalcopyrite, pyrite, digenite, and djurleite. ## Localities Key localities worldwide include: - I.S. Mine in Silverton, Colorado, USA (type locality). - Tsumeb Mine in Namibia. - Areas around Băița and Săcărâmb in Romania. - Akayama Mine in Japan.

Rarity

Rare

For collectors

## Quality Criteria The most highly valued specimens are those with visible, even small, but well-formed prismatic crystals, which are extremely rare. In the case of massive material, its value is determined by the richness of skinnerite aggregates and its association with other rare or visually attractive minerals. ## Popular Localities From a collector's perspective, the most famous specimens come from historical localities such as the Tsumeb mine in Namibia and deposits in Romania (Săcărâmb) and the USA (Colorado).

Care and storage

## Cleaning Skinnerite specimens should only be dry-cleaned, using a soft brush or compressed air to remove dust. Contact with water, and especially with chemicals, can lead to permanent damage or tarnishing. ## What to Avoid Avoid contact with water, acids, and other chemical agents. As a soft mineral (hardness 3), it is susceptible to scratches and therefore requires careful handling. Prolonged exposure to humid air can cause oxidation and tarnish formation. ## Storage It is recommended to store specimens in a dry place, preferably in closed, padded collector boxes or display cases. This protects the mineral from moisture, dust, and mechanical damage.

Sources

IMA Mineral List (CNMNC)