Sulphotsumoite
Chemical formula: Bi<sub>3</sub>Te<sub>2</sub>S
Sulfotsumoite is a rare bismuth sulfide and telluride, forming small, platy crystals with a metallic luster.
Description
## Characteristics Sulfotsumoite is a rare mineral from the sulfotelluride group, chemically a bismuth sulfide and telluride (Bi₃Te₂S). It typically occurs as small, irregular grains or platy, lamellar aggregates. It rarely forms well-developed, hexagonal, tabular crystals. Its appearance is typical for many ore minerals – it has a steel-gray to tin-white color and a strong, metallic luster. It is an opaque mineral. ## Physical Properties This mineral is relatively soft, with a Mohs hardness of approximately 3. It has a very high density of 8.16 g/cm³, which makes even small specimens surprisingly heavy. It possesses perfect cleavage in one direction, causing it to tend to split into thin plates or lamellae. The luster is strongly metallic, and the streak is grayish-black. ## Colors and Varieties Sulfotsumoite has a consistent, characteristic color in shades from steel-gray to tin-white, sometimes with a slight yellowish or creamy tint. No color or commercial varieties are distinguished. ## History and Name This mineral was first described in 1978 by Yoshimichi Shimazaki and Takeo Ozawa. Its name refers to its chemical composition – the presence of sulfur ("sulpho") – and to the mineral tsumoite, to which it is closely related. Tsumoite, in turn, took its name from its discovery locality, the Tsumo mine in Shimane Prefecture, Japan, which is also the type locality for sulfotsumoite. ## Uses Due to its rarity, sulfotsumoite has no industrial applications. It is solely an object of scientific interest and a prized acquisition for advanced systematic and ore mineral collections.
Diagnostic features
## Identification The identifying features of sulfotsumoite include its steel-gray color, strong metallic luster, high density, and perfect cleavage, which gives aggregates a platy or lamellar appearance. The streak is grayish-black. In field conditions, it is difficult to identify without specialized equipment. ## Distinguishing from Similar Minerals Sulfotsumoite is visually almost identical to many other bismuth tellurides and sulfosalts, such as tsumoite, tetradymite, tellurobismuthite, and joséite. Tsumoite (BiTe) does not contain sulfur, and tetradymite (Bi₂Te₂S) has a different bismuth-to-tellurium ratio. Definitive differentiation of these minerals is almost exclusively possible through chemical analysis (e.g., EDS) or X-ray methods (XRD). ## Crystal Forms It is most commonly found in the form of platy or lamellar aggregates and irregular grains embedded in rock. It rarely forms small, hexagonal tabular crystals, reaching at most a few millimeters in diameter.
Geological environment
## Genesis Sulfotsumoite is a hydrothermal mineral. It forms in ore veins developing under low to medium temperature conditions, usually in a paragenesis rich in bismuth, tellurium, gold, and sulfur. ## Mineral Associations This mineral often co-occurs with native bismuth, native gold, tsumoite, tetradymite, tellurobismuthite, joséite-A, joséite-B, pilsenite, as well as more common sulfides like pyrite and chalcopyrite. It is usually accompanied by quartz. ## Localities The most important and classic localities for this mineral include the Tsumo mine in Shimane Prefecture, Japan (type locality), the Dashuigou tellurium deposit in Sichuan Province, China, where rich specimens have been found, as well as the Glava mine in Värmland, Sweden, and the vicinity of Moctezuma in Sonora State, Mexico.
Rarity
Very rare
Collector aspects
## Quality Criteria The collector appeal of sulfotsumoite primarily depends on the richness of the specimen – the higher the concentration of the mineral on the matrix, the better. Specimens with visible, even if small, platy crystals are highly valued. The co-occurrence with other rare minerals, especially native bismuth or gold, is also of key importance. Specimens on a quartz matrix are the most desirable. ## Popular Localities Specimens from the Dashuigou deposit in China are considered the best in terms of quality and availability. Material from the type locality in Japan has great historical value but is extremely rare on the collector's market.
Care and storage
## Cleaning Sulfotsumoite specimens should be cleaned very carefully, preferably dry, using a soft brush to remove dust. If necessary, a moistened cotton swab with distilled water can be used, followed by immediate and thorough drying of the specimen. Avoid immersion in water. ## What to Avoid The mineral is soft and susceptible to scratches. It should be protected from contact with harder minerals. It is also sensitive to acids and other chemicals, which can cause etching or discoloration. Do not use ultrasonic cleaners or steam cleaning. ## Storage It is recommended to store specimens in separate, sealed boxes or display cases to prevent scratches and limit contact with moisture and airborne contaminants that could dull its surface. It is best kept under stable room conditions.