Vyalsovite
Chemical formula: CaFe²⁺AlS²⁻(OH)₅
Vyalsovite is an extremely rare calcium, iron, and aluminum sulfide and hydroxide, forming tiny, metallic grains in metamorphic rocks.
Properties
- Mohs hardness
- 4.5
- Color
- Carmine-red
- Luster
- Metallic
- Streak
- Black
- Density
- 0
- Cleavage
- None
- Fracture
- Uneven
- Transparency
- Opaque
- Crystal system
- Monoclinic
Diagnostic features
## Identification Identification of vyalsovite is possible only with advanced laboratory techniques. In practice, it involves optical analysis in reflected light (ore microscope), where it appears as fine, metallic, gray-creamy grains. Final confirmation requires chemical composition analysis (e.g., using an electron microprobe) and crystal structure analysis (X-ray diffraction). ## Distinguishing from Similar Minerals Vyalsovite coexists with other sulfides, such as pyrite, chalcopyrite, and molybdenite. In reflected light, it differs from them in color and optical properties (e.g., anisotropy). Pyrite is brighter and distinctly yellow, chalcopyrite has a more intense yellow color, and molybdenite exhibits strong pleochroism and anisotropy, which vyalsovite does not possess to the same extent. ## Crystal Forms Vyalsovite forms exclusively anhedral, i.e., irregular, imperfectly formed grains. They usually have rounded or irregular contours and occur as isolated inclusions in other minerals, mainly lazurite and diopside.
Geological environment
## Genesis Vyalsovite forms as a result of contact metamorphism processes. It forms in calc-silicate rocks (skarns) at the contact of alkaline syenite intrusions with dolomites. It is a product of metasomatism, a process of chemical transformation of rocks under the influence of hot solutions and gases rich in sulfur, iron, and aluminum. ## Mineral Associations This mineral occurs in close association with lazurite, in which it most often forms inclusions. It is also accompanied by other minerals typical of this environment, such as diopside, calcite, afghanite, phlogopite, pyrite, and molybdenite. ## Localities The only confirmed and described occurrence of vyalsovite in the world is its type locality – the Malo-Bystrinskoe lazurite deposit, located in the mountains on the western shore of Lake Baikal, in the Irkutsk Oblast of Russia.
Rarity
Extremely rare
For collectors
## Quality Criteria The quality of a vyalsovite specimen is assessed quite differently than for macroscopic minerals. Since it occurs as microscopic grains, the most important criterion is the abundance and size of these grains within the rock matrix. The most valuable samples are those where vyalsovite grains are numerous and clearly visible under a microscope. Association with well-formed, intensely blue lazurite is also important, enhancing the aesthetic appeal of the entire specimen. ## Popular Localities The only source of vyalsovite specimens is its discovery site: the Malo-Bystrinskoe deposit in Russia. All samples available on the collector's market come from this single locality, making them extremely rare and sought after by collectors specializing in systematic and rare minerals.
Care and storage
## Cleaning Due to the extreme rarity and microscopic size of grains embedded in the rock matrix, specimens containing vyalsovite should not be subjected to any invasive cleaning methods. Any attempts at mechanical or chemical cleaning can irreversibly destroy the mineral. Only gentle dusting of the matrix with a soft brush to remove dust is permissible. ## What to Avoid Avoid contact with any chemicals, acids, and bases. As a sulfide, the mineral is susceptible to oxidation and chemical reactions that can alter its composition and appearance. It should also be protected from moisture and sudden temperature changes. ## Storage Specimens containing vyalsovite, which are typically rock fragments (matrix), should be stored under stable conditions. It is best to place them in a closed, padded "micromount" box to protect them from mechanical damage and dust. Store in a dry place, away from direct sunlight.