Ottensite
Chemical formula: Na<sub>3</sub>(Sb<sup>3+</sup><sub>2</sub>O<sub>3</sub>)<sub>3</sub>(Sb<sup>3+</sup>S<sup>2-</sup><sub>3</sub>)·3H<sub>2</sub>O
Ottensite is a rare mineral from the sulfide and oxide group, forming characteristic, acicular crystals of an intense red color.
Properties
- Mohs hardness
- 1-2
- Luster
- Silky
- Streak
- Red
- Density
- 3.55
- Cleavage
- None
- Fracture
- Uneven
- Transparency
- Translucent
- Crystal system
- Trigonal
Diagnostic features
## Identification Ottensite is relatively easy to identify visually for a trained eye, provided its origin is known. Key features include its intense red color, silky luster, and the form of very thin, acicular or hair-like crystals forming tangled aggregates. Its extreme delicacy is also a characteristic feature. ## Distinguishing from Similar Minerals It can be confused with other red, acicular antimony minerals, such as kermesite (Sb₂S₂O) or getchellite (AsSbS₃). However, kermesite usually forms thicker, radial crystal aggregates. Getchellite has a similar color but is harder and occurs in different associations. Final differentiation requires advanced chemical (EDS) or X-ray (XRD) analyses. ## Crystal Forms Crystals are always acicular or hair-like (filiform habit), very elongated along one axis. They form dense, tangled aggregates resembling felt or mineral wool, as well as small radial aggregates.
Geological environment
## Genesis Ottensite is a secondary mineral, forming in the oxidation zones of hydrothermal antimony deposits. It forms as a result of weathering and alteration of primary antimony sulfides, mainly stibnite, under low-temperature conditions. ## Mineral Associations It most often co-occurs with the mineral from which it forms, namely stibnite. It is also accompanied by other secondary antimony minerals, such as valentinite, senarmontite, kermesite, and stibiconite. It often grows on quartz or calcite gangue rocks. ## Localities The only confirmed and described occurrence of ottensite in the world is its type locality - the Xikuangshan antimony deposit, in Lengshuijiang Prefecture, Hunan Province, China. This is the largest antimony deposit in the world.
Rarity
Very rare
For collectors
## Quality Criteria The most important criterion for evaluating an ottensite specimen is the intensity and saturation of its red color. Specimens with abundant, well-formed, and undamaged delicate, acicular aggregates are highly valued. The contrast with a light matrix rock (most often quartz) also significantly enhances the visual appeal and value of the specimen. Due to extreme fragility, the state of preservation is crucial. ## Popular Localities All collector specimens come from a single location in the world: the Xikuangshan mine in China. This is the only known locality for this mineral.
Care and storage
## Cleaning Ottensite specimens should generally not be cleaned. They are extremely fragile, and any attempt at mechanical cleaning (even with a soft brush) or using liquids will almost certainly destroy the delicate, acicular crystals. They should be left undisturbed. ## What to Avoid Absolutely everything should be avoided: touching, vibrations, temperature changes, humidity, and direct sunlight, which can cause color fading. Chemicals, including water, can damage the mineral. ## Storage Ottensite specimens require storage in a sealed, stable "micromount" type container, away from vibrations, dust, and light. It is best to display them under glass or in dedicated showcases for delicate minerals to minimize the risk of damage from accidental touch or air movement.