Sergeevite
Chemical formula: Ca<sub>2</sub>Mg<sub>11</sub>(CO<sub>3</sub>)<sub>9</sub>(HCO<sub>3</sub>)<sub>4</sub>(OH)<sub>4</sub>·6H<sub>2</sub>O
Sergeevite is a very rare, hydrated calcium and magnesium carbonate, forming fine, spherulitic aggregates of white color.
Properties
- Mohs hardness
- 1
- Luster
- Silky
- Streak
- White
- Density
- 2.43
- Cleavage
- None
- Fracture
- Uneven
- Transparency
- Translucent to opaque
- Crystal system
- Trigonal
Diagnostic features
## Identification Sergeevite is difficult to identify without advanced research methods. It is distinguished by its occurrence as white, radial or spherulitic aggregates with a silky luster. A key diagnostic feature is its extreme softness (hardness 1) and vigorous reaction with dilute hydrochloric acid. Final identification requires X-ray diffraction (XRD) or chemical analysis. ## Distinguishing from Similar Minerals It can be confused with other white, fibrous carbonates or sulfates, such as artinite, dypingite, or gypsum. It differs from artinite and dypingite in chemical composition (presence of calcium) and crystallographic properties. It is distinguished from gypsum by its vigorous reaction with acid. ## Crystal Forms It forms radial aggregates and spherulites up to 2-3 mm in diameter. These aggregates consist of very fine, elongated crystals with a bladed or fibrous habit.
Geological environment
## Genesis Sergeevite is a secondary mineral, forming in the weathering zones of silicate-borate deposits in ultramafic rocks (serpentinites). It forms as a result of low-temperature processes, likely due to the interaction of carbonate-rich waters with magnesium- and calcium-rich rocks. ## Mineral Associations This mineral occurs in association with other rare magnesium carbonates and borates, such as dypingite, hydromagnesite, artinite, as well as with calcite, dolomite, and boron minerals. ## Localities The only confirmed and described occurrence of sergeevite in the world is its type locality – the Akyar boron deposit in the Aktobe region of Kazakhstan.
Rarity
Extremely rare
For collectors
## Quality Criteria As an extremely rare mineral, every sergeevite specimen is valuable to specialized collectors of rare and systematic minerals. The most desirable specimens are those with well-formed, distinct spherulites or rich coatings on the host rock. Contrast with a darker substrate (e.g., serpentinite) enhances visual appeal. Purity and lack of damage to delicate aggregates are crucial. ## Popular Localities The only source of specimens is the type locality in Kazakhstan, which makes material on the collector's market virtually unavailable.
Care and storage
## Cleaning Due to its extreme softness (Mohs hardness 1) and solubility in acids, mechanical and chemical cleaning is highly inadvisable. Specimens should be protected from dust by storing them in closed containers. If cleaning is absolutely necessary, a very soft brush can be used very carefully to remove loose particles. ## What to Avoid Contact with water and all chemicals, especially acids, which cause rapid dissolution of the mineral with the release of carbon dioxide, should be avoided. The mineral is very soft and brittle, susceptible to mechanical damage with the slightest touch. It should be protected from high temperatures and changes in humidity. ## Storage Sergeevite specimens should be stored under stable conditions, in a dry place, preferably in a tightly sealed "micromount" box, to protect them from dust, moisture, and physical damage.