Chelkarite

Chemical formula: CaMgB₂O₄Cl₂·₇H₂O

Chelkarite is a rare hydrated calcium and magnesium borate, forming fibrous aggregates of white color.

## Characteristics Chelkarite is a mineral from the borate group, characterized by a complex chemical composition containing calcium, magnesium, chlorine, and water. It occurs as fibrous or radial aggregates, which can form compact or earthy masses. Individual "fibers" are actually elongated, acicular crystals. It is typically white or colorless, with a silky luster on the surfaces of fibrous aggregates. ## Physical Properties This mineral is relatively soft, with a Mohs hardness of 2.5. Its fibrous structure makes it brittle. The luster is described as silky for aggregates and vitreous on rarely observed crystal faces. It is a light mineral, with a density of approximately 1.99 g/cm³. ## Colors and Varieties Chelkarite is usually white, grayish-white, or colorless. No colored or commercial varieties have been distinguished. ## History and Name The mineral's name comes from its discovery locality – the Chelkar salt deposit region in western Kazakhstan. It was first described in 1963 by W. M. Bojko.

Properties

Mohs hardness: 2.5
Luster: Silky
Streak: White
Density: 1.99
Cleavage: Perfect on {010}, good on {100}
Fracture: Splintery
Transparency: Translucent
Crystal system: Orthorhombic

Diagnostic features

## Identification Chelkarite is primarily identified by its characteristic fibrous or radial aggregate forms, white color, and silky luster. A key feature is its occurrence in salt evaporites. It is soft and easily scratched. It reacts with water. ## Distinguishing from Similar Minerals It can be confused with other fibrous minerals found in similar environments, such as ulexite or colemanite. Ulexite often exhibits the characteristic "television stone" effect, which is absent in chelkarite. Final distinction from other white, fibrous borates usually requires advanced analytical methods, such as X-ray diffraction (XRD). ## Crystal Forms It forms acicular, elongated crystals that almost always occur as compact, fibrous, or radial aggregates.

Geological environment

## Genesis Chelkarite is a mineral of sedimentary origin. It forms as a result of evaporation of waters in salt basins, in a dry and hot climate. It is a product of the alteration of other borate minerals within Zechstein salt domes. ## Mineral Associations It most commonly co-occurs with other evaporite minerals, such as halite, sylvite, bischofite, boracite, as well as gypsum and anhydrite. ## Localities The most important and classic locality, from which most known specimens originate, is the Chelkar salt deposit in the West Kazakhstan Region, Kazakhstan. This is its type locality.

Rarity

Very rare

For collectors

## Quality Criteria The most valuable chelkarite specimens are those that show well-formed, radial aggregates with a distinct, fibrous structure and a clean, white color. The size of the specimen and its state of preservation, without mechanical damage, are also important. Due to its rarity, any well-identified specimen has value for collectors specializing in mineral systematics or borate minerals.

Care and storage

## Cleaning Chelkarite specimens should only be cleaned mechanically, dry, using a soft brush. Due to its water solubility, contact with any liquid is absolutely not recommended. ## What to Avoid Avoid contact with water, acids, and other chemicals that can damage or dissolve it. The mineral is sensitive to humidity changes – in dry air, it can lose water and transform into other mineral phases. It should be protected from high temperatures and direct sunlight. ## Storage It is recommended to store specimens in airtight, sealed containers (e.g., "membrane boxes" or sealed boxes) to maintain a stable humidity level. They should be displayed away from heat and light sources.

Sources

IMA Mineral List (CNMNC)