Simonite
Chemical formula: Tl¹⁺Hg²⁺As³⁺₃S²⁻₆
Simonite is a rare, dark red to black thallium, mercury, and arsenic sulfide, forming tiny, tabular crystals.
Properties
- Mohs hardness
- 1.5-2
- Color
- Red
- Luster
- Metallic
- Streak
- Red-brown
- Density
- 0
- Cleavage
- Perfect on {100}
- Fracture
- Uneven
- Transparency
- Opaque
- Crystal system
- Monoclinic
Diagnostic features
## Identification Identification of simonite is almost exclusively possible using advanced laboratory methods, such as chemical composition analysis (EDS) and X-ray diffraction analysis (XRD). Visually, under microscopic magnification, characteristic features include very small, tabular crystals of black or dark red color with strong, red internal reflections and a metallic luster. ## Distinguishing from Similar Minerals Simonite can be confused with other rare sulfosalts from the same locality, such as lorandite, imhofite, or wallisite. Distinguishing it from these without specialized analysis is practically impossible. All these minerals form similar, small, dark crystals in the same rock (Binn Valley). ## Crystal Forms Simonite crystals are very small, typically up to 1 mm in length. They adopt tabular or platy forms, often flattened. They crystallize in the monoclinic system.
Geological environment
## Genesis Simonite forms as a result of hydrothermal processes in ore deposits. It occurs in dolomitic carbonate rocks (so-called Sachsel dolomites) that have undergone low-grade metamorphism. ## Mineral Associations This mineral co-occurs with other rare arsenic and thallium sulfosalts. In the type locality (Lengenbach mine), it was found in association with realgar, orpiment, sartorite, baumhauerite, rathite, hatchite, and pyrite. ## Localities The only confirmed occurrence of simonite in the world is the Lengenbach quarry in the Binn Valley (Binnatal) in the canton of Valais, Switzerland. This is the type locality for this mineral.
Rarity
Extremely rare
For collectors
## Quality Criteria The quality of a simonite specimen is assessed primarily based on the size and development of its crystals, which is a rarity. Specimens with clearly visible, sharp crystals, even if microscopic in size, are most valued. Aesthetic composition with associated minerals is also important, especially if simonite is well-exposed on the rock matrix. ## Popular Localities The only source of simonite specimens is the Lengenbach quarry in Switzerland. All specimens available on the collector's market originate from this single, historical locality.
Care and storage
## Cleaning Simonite specimens, typically microminerals, should not be cleaned mechanically or chemically. Any attempts at cleaning may irreversibly damage the delicate crystals. If dust removal is necessary, a gentle stream of compressed air can be used from a safe distance. ## What to Avoid Avoid contact with any chemicals, acids, and detergents. The mineral is very soft and brittle, so it should be protected from impacts, scratches, and vibrations. Due to its thallium, mercury, and arsenic content, it is toxic – direct skin contact should be avoided, and hands should be thoroughly washed after any contact. It must not be heated or ingested. ## Storage Simonite specimens should be stored exclusively in specialized micromount boxes, away from dust, moisture, and direct sunlight. It is essential to clearly label the box with information about the mineral's toxicity.