Joséite-C

Chemical formula: Bi₁₆Te₃S₉

A rare bismuth tellurosulfide, forming small, metallic flakes and aggregates, found in hydrothermal veins.

## Characteristics Joséite-C is a rare sulfide mineral, more specifically a bismuth tellurosulfide. It usually occurs as small, irregular flakes, scales, or granular aggregates embedded in rock. It rarely forms imperfect crystals with a hexagonal outline. Its appearance is typically metallic, with a silvery-white color that may tarnish in air, taking on a grayish-yellow or brownish hue. ## Physical Properties This mineral is soft and heavy. It is characterized by a metallic luster and is opaque. It possesses perfect cleavage in one direction, which allows it to easily split into thin, slightly flexible flakes. ## Colors and Varieties Joséite-C is tin-white to silvery-white, often with a yellowish or brownish tarnish. No color or commercial varieties are distinguished. ## History and Name The name "joséite" comes from its original discovery locality in the São José mine (now in the municipality of Ouro Preto) in Brazil. The letter "-C" in the name refers to a specific polytype in the joséite group mineral series, defined based on crystallographic studies. The entire joséite group (A, B, C) was characterized in the mid-20th century, although joséite itself was known earlier.

Properties

Mohs hardness: 1.5-2
Luster: Metallic
Streak: Greyish black
Density: 8.14
Cleavage: Perfect on {0001}
Fracture: Uneven
Transparency: Opaque
Crystal system: Trigonal

Diagnostic features

## Identification Joséite-C is identified by its metallic luster, silvery-white color, very high density, and perfect cleavage, which allows for the separation of thin, flexible flakes. It is very soft and can be scratched with a fingernail. ## Distinguishing from Similar Minerals It can be confused with other bismuth tellurides and sulfides, such as tetradymite, tellurobismuthite, or other minerals from the joséite group. Final distinction from these minerals requires advanced analytical methods, such as X-ray diffraction (XRD) or chemical analysis (EDS/WDS). ## Crystal Forms It most commonly occurs as irregular, platy or scaly aggregates. Rarely, it forms poorly developed, tabular crystals with a hexagonal outline.

Geological environment

## Genesis Joséite-C is a hydrothermal mineral. It forms in quartz veins associated with igneous rock intrusions, under medium and high-temperature conditions. It is also found in skarns and gold deposits. ## Mineral Associations It often co-occurs with native bismuth, bismuthinite, native gold, pyrite, chalcopyrite, arsenopyrite, tetradymite, as well as quartz and various carbonates. ## Localities Key localities worldwide include: Ouro Preto in Brazil (type locality for the joséite group), Glacier Gulch in British Columbia (Canada), Hedley Mascot mine in British Columbia (Canada), as well as occurrences in the Bispberg area in Sweden and in Japan.

Rarity

Very rare

For collectors

## Quality Criteria For collectors, the most valuable specimens are those with well-formed, though rare, crystals or rich platy aggregates clearly visible in the matrix. Surface purity and absence of tarnish also increase the specimen's value. Associations with other rare minerals, especially native gold, are particularly prized.

Care and storage

## Cleaning Specimens should only be cleaned mechanically, using a soft brush to remove dust. Due to its softness and perfect cleavage, all contact with water and chemicals should be avoided, and the mineral should be handled with extreme care. ## What to Avoid Avoid contact with water, acids, and other chemicals that can damage the mineral's surface. It must be protected from moisture, high temperatures, and direct sunlight, which can accelerate tarnishing. Due to its softness, it is very susceptible to scratches. ## Storage Joséite-C specimens are best stored in closed, dry containers or display cases, away from other minerals that could scratch them. Avoid storage in humid conditions to prevent oxidation.

Sources

IMA Mineral List (CNMNC)