Shimenite
Chemical formula: Tl<sup>1+</sup><sub>5</sub>Sb<sup>3+</sup><sub>21-y</sub>As<sup>3+</sup><sub>y</sub>S<sup>2-</sup><sub>34</sub> (9 ≤ y ≤ 10)
Shimenite is a very rare, lead-gray thallium, antimony, and arsenic sulfosalt, forming tiny, acicular crystals.
Properties
- Luster
- Metallic
- Streak
- Black
- Cleavage
- Good on {100}
- Fracture
- Uneven
- Transparency
- Opaque
- Crystal system
- Monoclinic
Diagnostic features
## Identification Identifying shimenite is extremely difficult without advanced analytical methods. Visually, it is characterized by occurring in the form of very fine, acicular, lead-gray crystals with a metallic luster. Key to identification is its co-occurrence with other sulfosalts in a specific geological environment (gold and arsenic deposits). ## Distinguishing from Similar Minerals Shimenite can be confused with many other acicular sulfosalts, such as stibnite, lorandite, or other minerals from the pierrotite group. Certain differentiation is almost exclusively possible using chemical analysis (EDS) or X-ray diffraction (XRD), which allow for determining its unique composition with a dominance of thallium, antimony, and arsenic. ## Crystal Forms Shimenite forms elongated, acicular or hair-like crystals, stretched along the [010] axis. These crystals often occur as tangled, felt-like masses or radial aggregates intergrown with other minerals, mainly calcite.
Geological environment
## Genesis Shimenite is a low-temperature hydrothermal mineral. It forms in the final stages of crystallization in calcite veins, cutting through gold, arsenic, and mercury deposits embedded in siliceous rocks. ## Mineral Associations This mineral co-occurs with other sulfosalts and sulfides. In its type locality (Shimen, China), it was found in association with realgar, orpiment, stibnite, getchellite, wakabayashilite, laffittite, pierrotite, parapierrotite, erniggliite, calcite, and quartz. ## Localities The only confirmed and thoroughly described occurrence of shimenite in the world is its type locality: the Jiepaiyu gold deposit in the Shimen arsenic mine, Shimen County, Changde Prefecture, Hunan Province, China.
Rarity
Extremely rare
For collectors
## Quality Criteria The quality of a shimenite specimen is primarily assessed based on the abundance and development of microscopic crystals. The most valued specimens are those showing dense clusters or distinct, individual shimenite needles, ideally contrasting with a light background, e.g., white calcite. Due to the microscopic nature of the mineral, the quality of the microphotograph is crucial. ## Popular Localities The only source of shimenite specimens is its type locality in the Shimen mine in China. All specimens available on the collector's market originate from this single location.
Care and storage
## Cleaning Shimenite specimens, due to their delicacy and microscopic size, should generally not be mechanically cleaned. If absolutely necessary, compressed air (from a safe distance) can be used to remove dust. Contact with water and any chemicals should be avoided. ## What to Avoid Contact with acids and other chemical agents that can destroy the mineral must be strictly avoided. The crystals are very brittle and susceptible to mechanical damage. Due to its thallium and arsenic content, the mineral is toxic – avoid inhaling dust and wash hands after any contact. ## Storage Shimenite specimens should be stored under stable conditions, in sealed "micromount" containers, to protect them from dust, moisture, and physical damage. They should be kept away from direct sunlight and heat sources.