Yaroslavite

Chemical formula: Ca<sub>3</sub>Al<sub>2</sub>F<sub>10</sub>(OH)<sub>2</sub>·H<sub>2</sub>O

Jaroslavite is a rare hydrated calcium aluminum fluoride, forming tiny, colorless or white crystals and aggregates.

## Characteristics Jaroslavite is a mineral from the halide group, specifically a hydrated calcium aluminum fluoride. It occurs as very small, tabular or platy crystals, rarely exceeding 1 mm. Most often, it forms compact, earthy or chalk-like aggregates, as well as spherulitic or radial clusters. It is a colorless or white mineral with a vitreous or dull luster. ## Physical Properties Jaroslavite crystals exhibit a hardness of approximately 3.5 on the Mohs scale. They are brittle and have a density of 2.92 g/cm³. The mineral's luster is described as vitreous, and in the case of earthy aggregates, dull. It is transparent to translucent. ## History and Name The mineral was first described in 1966 by A. A. Novikova. Its name comes from the Russian city of Yaroslavl (Ярославль), in whose honor it was named. ## Uses Due to its rarity and small crystal size, jaroslavite has no industrial application and is solely an object of interest for collectors specializing in rare minerals and scientists.

Properties

Mohs hardness
3.5
Luster
Vitreous
Streak
White
Density
2.92
Cleavage
Perfect on {010}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Orthorhombic

Diagnostic features

## Identification Amateur identification of jaroslavite is practically impossible due to its appearance and small size. It usually occurs as white, earthy coatings or very fine crystals. Definitive identification requires advanced analytical methods, such as X-ray diffraction (XRD) or chemical analysis (EDS/WDS). ## Distinguishing from Similar Minerals It can be confused with many other secondary fluoride minerals, such as cryolite, ralstonite, pachnolite, or gearksutite, as well as with calcite or gypsum. Distinguishing it from these without specialized equipment is unfeasible. Checking co-occurring minerals and the geological context of the find is crucial. ## Crystal Forms Jaroslavite crystallizes in the orthorhombic system. It forms very small, thin, tabular crystals with a hexagonal outline. It is most commonly found in the form of radial or spherulitic aggregates, as well as compact, earthy or chalk-like masses.

Geological environment

## Genesis Jaroslavite is a secondary mineral, forming in the weathering (oxidation) zones of polymetallic deposits, especially those rich in fluorite. It forms as a result of hydrothermal solutions acting on rocks containing aluminosilicates and fluorite. It can also form in pegmatites. ## Mineral Associations It most commonly co-occurs with fluorite, cryolite, ralstonite, pachnolite, gearksutite, as well as with quartz, calcite, and clay minerals. ## Localities The most important and classic localities for this mineral are in Russia, including the Yaroslavl region (type locality) and the Urals. It has also been reported in the Czech Republic (Krupka in the Ore Mountains), Germany (Saxony), and the USA (Colorado).

Rarity

Very rare

For collectors

## Quality Criteria The most desired specimens by collectors are those with visible, well-formed microcrystals of jaroslavite, forming radial aggregates or rosettes on a contrasting rock matrix. Since the mineral is usually white or colorless, its value is primarily determined by the quality and form of the crystals, rather than color. Large, rich clusters on matrix are significantly more valuable than loose material or compact masses. ## Popular Localities Specimens from the type locality in Russia and from historical localities in the Czech Republic and Germany are prized by collectors specializing in mineral systematics.

Care and storage

## Cleaning Jaroslavite specimens should be cleaned very carefully, only using a soft brush to remove dust. Due to its reactivity with water and acids, all wet cleaning should be avoided. ## What to Avoid Contact with water, which can damage or dissolve the mineral, must be strictly avoided. Contact with acids and other chemicals is also not recommended. As a relatively soft and brittle mineral, it is susceptible to mechanical damage. ## Storage Collector specimens of jaroslavite, especially those with well-formed microcrystals, should be stored in sealed, closed "micromount" boxes, which protect them from dust, moisture, and mechanical damage.

Sources

Read more