Dobrovolskyite
Chemical formula: Na₄Ca(S⁶⁺O₄)₃
Dobrowolskite is a rare sodium calcium sulfate, forming colorless, tabular crystals in volcanic sublimation products.
Properties
- Mohs hardness
- 3.5
- Luster
- Vitreous
- Streak
- White
- Density
- 2.68
- Fracture
- Conchoidal
- Transparency
- Transparent
- Crystal system
- Trigonal
Diagnostic features
## Identification Field identification of dobrowolskite is practically impossible. Identification requires advanced analytical methods, such as Raman spectroscopy and chemical analysis using an electron microprobe (EDS/WDS). Its chemical composition and occurrence in the specific environment of volcanic fumaroles are characteristic. ## Distinguishing from similar minerals It can be confused with other colorless sulfates found in similar environments, such as thenardite (Na₂SO₄) or anhydrite (CaSO₄). Differentiation is based solely on precise chemical analysis, which reveals the presence of both sodium and calcium in specific proportions. ## Crystal forms Dobrowolskite forms very small, thin, tabular crystals with a hexagonal outline. These crystals occur as single flakes or form small, loose aggregates and clusters.
Geological environment
## Genesis Dobrowolskite is a mineral of volcanic origin. It forms through sublimation from volcanic gases at high temperatures (above 400°C) in active fumarole fields. It crystallizes directly from the gas phase on the surface of lava or in its small fissures. ## Mineral associations This mineral coexists with other sulfates and halides formed under similar conditions. It is most commonly associated with: aphthitalite, langbeinite, hematite, thenardite, halite, sylvite, and newly discovered, rare minerals such as arcanite, dravertite, and filatovite. ## Localities The only confirmed locality for dobrowolskite in the world is its type locality – Arsenievskaya fumarole on the second cinder cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption (1975-1976) at Tolbachik volcano, Kamchatka, Russia.
Rarity
Extremely rare
For collectors
## Quality criteria As a "micromount" mineral, the collector's value of a specimen depends on the presence of well-formed, albeit microscopic, crystals that can be identified and observed under magnification. The most valuable specimens are those where dobrowolskite crystals are clearly visible on the rock matrix and well-separated from other minerals. The richness of association with other rare sulfates also increases its scientific and collector's value. ## Popular localities The only source of dobrowolskite specimens is its discovery site at Tolbachik volcano in Kamchatka. Material from this locality is extremely rare on the collector's market and primarily goes to scientific institutions and specialized systematic mineral collections.
Care and storage
## Cleaning Due to its extreme rarity and fragility, dobrowolskite specimens should not be cleaned mechanically or chemically. Any impurities should be left intact to avoid damaging the microscopic crystals. ## What to avoid The mineral is water-soluble, so contact with water and moisture must be absolutely avoided. It should also be protected from all chemicals, ultrasound, and sudden temperature changes. ## Storage Specimens should be stored in a sealed, dry container, preferably in a specialized "micromount" box, away from sources of moisture. Storage in conditions of controlled, low humidity is crucial for maintaining the mineral's integrity.