Solongoite

Chemical formula: Ca<sub>2</sub>B<sub>3</sub>O<sub>4</sub>(OH)<sub>4</sub>Cl

Solongoite is a very rare calcium borate, forming colorless or white, tabular crystals with a pearly luster.

## Characteristics Solongoite is a hydrated calcium borate with chlorine, belonging to the group of very rare minerals. It occurs as small, tabular or platy crystals, often aggregated into radial or fibrous forms. Individual crystals rarely exceed 1 mm in size. It is a colorless or white mineral, with a characteristic pearly luster on cleavage surfaces. ## Physical Properties This mineral is relatively soft, with a Mohs hardness of 3.5. It is light, with a density of approximately 2.5 g/cm³. It exhibits perfect cleavage in one direction, causing it to easily split into thin lamellae or fibers. The luster is pearly on cleavage planes and vitreous on other surfaces. It is transparent to translucent. ## Colors and Varieties Solongoite is typically colorless or white. No color or commercial varieties are distinguished. ## History and Name The mineral's name comes from its discovery locality – the Solongo boron deposit in Buryatia (Russia). It was described and approved as a new mineral by the International Mineralogical Association (IMA) in 1974. The first description was made by a group of Russian mineralogists led by S.V. Malinko. ## Applications Due to its extreme rarity and small crystal size, solongoite has no industrial applications. It is of purely scientific and collector's interest, being a coveted object for specialized collectors of rare minerals.

Properties

Mohs hardness
3.5
Luster
Pearly
Streak
White
Density
2.5
Cleavage
Perfect on {001}
Fracture
Splintery
Transparency
Transparent to translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Solongoite can be identified by its habit – small, tabular crystals aggregated into radial forms. Key features include a pearly luster on perfect cleavage surfaces, low hardness, and its association with borate minerals in skarns. ## Distinguishing from Similar Minerals It may be confused with other white, fibrous, or platy borate minerals or zeolites. Its co-occurrence with other borates distinguishes it from zeolites. Accurate identification requires advanced research methods, such as X-ray diffraction (XRD) or chemical analysis. ## Crystal Forms Crystals are tabular or platy, with a hexagonal outline. They usually form radial, fibrous, or spherulitic aggregates. Less commonly, they occur as scattered, individual lamellae on the rock matrix.

Geological environment

## Genesis Solongoite is a hydrothermal mineral associated with metasomatic processes. It forms in magnesian skarns that have undergone subsequent boron enrichment. It develops in contact zones between magmatic intrusions and carbonate rocks (dolomites). ## Mineral Associations This mineral co-occurs with other borates, such as kurchatovite, svabite, ludwigite, as well as with calcite, dolomite, fluorite, and magnetite. This paragenesis is characteristic of the Solongo deposit. ## Localities The only confirmed and well-studied locality for solongoite worldwide is its type locality – the Solongo boron deposit, in the Republic of Buryatia, Russia.

Rarity

Very rare

For collectors

## Quality Criteria The most prized specimens by collectors are those with well-formed, radial aggregates of solongoite, contrasting with a darker rock matrix. The size of the aggregates and the absence of mechanical damage significantly increase the specimen's value. Due to its rarity, even microscopic but well-formed crystals are considered valuable. ## Popular Localities The only source of collector specimens is the Solongo deposit in Russia. Material from this locality is very difficult to acquire on the market.

Care and storage

## Cleaning Due to its perfect cleavage and low hardness, solongoite specimens require very careful handling. Cleaning should be kept to a minimum. If necessary, a soft brush can be used to remove dust. Avoid water and any chemical agents. ## What to Avoid Absolutely avoid contact with water, acids, and other chemicals that may react with the mineral. Do not subject it to ultrasonic or steam cleaning. It is susceptible to mechanical damage, so it must be protected from scratching and impacts. ## Storage Solongoite specimens are best stored in stable conditions, in a sealed "micromount" box that protects against dust and mechanical damage. Avoid environments with high humidity.

Sources

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