Oscarkempffite

Chemical formula: Ag₁+₁₀Pb₂+₄(Sb₃+₁₇Bi₃+₉)S₂-₄₈

Oscarkempffite is a rare lead-silver antimony bismuth sulfide, forming acicular crystals with a metallic luster.

## Characteristics Oscarkempffite is a complex sulfosalt mineral of lead, silver, antimony, and bismuth. It occurs as elongated, acicular or bladed crystals, which can reach up to 2 mm in length. These crystals often form clusters or aggregates. The mineral is opaque and has a metallic luster and a steel-gray to black color. ## Physical Properties The mineral is characterized by a metallic luster and a black streak. Its Mohs hardness is approximately 3.5, and its density calculated from the chemical formula is 5.63 g/cm³. It is a brittle mineral. ## History and Name Oscarkempffite was first described in 2008 by S. Paar, D. Topa, W. H. Makovicky, and E. Makovicky. The name honors Professor Oscar Kempff (1836–1890), former director of the Potosí mine in Bolivia, in recognition of his contribution to Bolivian mining. ## Uses Due to its rarity, Oscarkempffite has no industrial application and is solely of interest to collectors and scientists studying sulfosalts.

Properties

Mohs hardness: 3.5
Luster: Metallic
Streak: Black
Density: 5.63
Cleavage: Not observed
Fracture: Undetermined
Transparency: Opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Key diagnostic features include the crystal habit – long, thin needles or blades with a steel-gray color and metallic luster. Its occurrence in paragenesis with other sulfosalts in Bolivian deposits is also an important clue. Final identification requires advanced methods such as chemical analysis (EDS/WDS) and X-ray diffraction (XRD). ## Distinguishing from Similar Minerals Oscarkempffite can be confused with other acicular sulfosalts, such as jamesonite, boulangerite, or zinkenite. Distinguishing it with the naked eye is practically impossible and requires laboratory analysis to determine the exact chemical composition, especially the proportions of Ag, Pb, Sb, and Bi. ## Crystal Forms The mineral forms elongated, prismatic crystals with an acicular or bladed habit. Crystals are often grouped into chaotic or radial aggregates.

Geological environment

## Genesis Oscarkempffite is a hydrothermal mineral. It forms in polymetallic ore veins, developing under low to medium temperature conditions. It is one of many complex sulfosalts that crystallize during the late stages of mineralization. ## Mineral Associations This mineral co-occurs with other sulfosalts, such as andorite, fizélyite, ramdohrite, owyheeite, miargyrite, diaphorite, as well as with pyrite, sphalerite, galena, stannite, and quartz. ## Localities The only confirmed occurrence (type locality) of Oscarkempffite is the San José mine in the Oruro Department, Bolivia.

Rarity

Very rare

For collectors

## Quality Criteria The most prized Oscarkempffite specimens are those with well-formed, undamaged, long crystals, forming aesthetic aggregates on a contrasting rock matrix, for example, on quartz. The presence of rare associated minerals is also important, as it increases the scientific and collector value of the specimen. ## Popular Localities The only known source of specimens is the historic San José mine in Oruro, Bolivia, which makes every specimen from this locality unique.

Care and storage

## Cleaning Due to its acicular form and brittleness, mechanical cleaning is highly inadvisable. Specimens should only be cleaned with compressed air to remove dust. Contact with water and any chemicals should be avoided. ## What to Avoid The mineral is sensitive to mechanical damage. Avoid vibrations, impacts, and contact with harder minerals. It should not be heated or exposed to acids and other chemical agents. ## Storage Oscarkempffite specimens should be stored in stable, sealed containers (e.g., "micromount boxes"), lined with soft material, to protect delicate crystals from damage and dust. Avoid areas with high humidity.

Sources

IMA Mineral List (CNMNC)