Ottemannite
Chemical formula: Sn<sup>2+</sup>Sn<sup>4+</sup>S<sup>2-</sup><sub>3</sub>
Ottemannite is a rare tin sulfide, forming tiny, acicular crystals with a metallic luster, found in hydrothermal deposits.
Properties
- Luster
- Metallic
- Streak
- Black
- Cleavage
- Good on {010}
- Fracture
- Uneven
- Transparency
- Opaque
- Crystal system
- Orthorhombic
Diagnostic features
## Identification Identification of ottemannite is based on its characteristic form – tiny, acicular crystals forming radial or tangled aggregates. The metallic, steel-gray luster is also a helpful feature. Definitive identification is almost exclusively possible using advanced analytical methods, such as X-ray diffraction (XRD) or X-ray microanalysis (EDS/WDS). ## Distinguishing from Similar Minerals Ottemannite can be confused with other acicular sulfides, such as stibnite, jamesonite, or boulangerite. Distinguishing it with the naked eye is practically impossible. Ottemannite is usually much finer, and its crystals are thinner and more delicate than those of the aforementioned minerals. Co-occurrence with other tin minerals, such as cassiterite, can be a diagnostic clue. ## Crystal Forms This mineral exclusively forms acicular or capillary crystals, often grouped into radial, stellate, or haphazardly tangled aggregates. It less commonly occurs as thin blades.
Geological environment
## Genesis Ottemannite is a mineral of hydrothermal origin. It forms during the final stages of crystallization in tin-rich ore veins, under low to medium temperature conditions. It is one of the last sulfides to crystallize from hydrothermal solutions. ## Mineral Associations It most commonly co-occurs with other tin minerals, such as cassiterite, stannite, and teallite. It is also accompanied by pyrite, quartz, stibnite, and cylindrite. ## Localities The most important and historical locality for ottemannite is Cerro de Potosí in the Potosí Department, Bolivia, from which the best-known specimens originate. It has also been found in tin mines in Hyōgo Prefecture, Japan, and in a few other rare localities worldwide.
Rarity
Very rare
For collectors
## Quality Criteria The most prized ottemannite specimens are those with well-formed, rich aggregates of acicular crystals, forming aesthetic, radial or "hedgehog-like" shapes. Contrast with a light matrix, such as quartz, significantly enhances visual appeal. Due to the microscopic size of the crystals, specimens are primarily evaluated under magnification. The size and richness of the aggregate are key factors influencing value. ## Popular Localities Specimens from the type locality – Cerro de Potosí in Bolivia – are by far the most sought after by collectors. Specimens from Japan are also valued, but much rarer on the market.
Care and storage
## Cleaning Ottemannite specimens are extremely delicate due to their acicular crystal habit. Mechanical cleaning is not recommended. If absolutely necessary, compressed air can be used from a safe distance to remove dust. Avoid contact with water and any chemicals. ## What to Avoid Avoid ultrasonic cleaners, steam cleaners, acids, solvents, and sudden temperature changes. The crystals are very brittle and fragile, so the specimen should be protected from shocks and impacts. ## Storage It is recommended to store specimens in sealed "micromount" boxes to protect them from dust and mechanical damage. Avoid exposure to humid air, which can cause slow oxidation.