Carboborite

Chemical formula: Ca₂Mg[B(OH)₄]₂(CO₃)₂·₄H₂O

Hydrated calcium and magnesium carbonate-borate, forming colorless, prismatic crystals with perfect cleavage.

## Characteristics Carboborite is a hydrated calcium and magnesium carbonate-borate. This mineral forms colorless, elongated crystals with a prismatic or acicular habit, often gathered into radial or chaotic aggregates. Specimens are typically small, with individual crystals rarely exceeding a few millimeters in length. It is a brittle mineral. ## Physical properties Carboborite is very soft, with a Mohs hardness of 2. It has a relatively low density, approximately 2.12 g/cm³. It is characterized by a vitreous luster and is usually translucent. It possesses perfect cleavage in one direction. ## Colors and varieties This mineral is usually colorless. No colored varieties or commercial names are distinguished for it. ## History and name Carboborite was first described in 1964. Its name refers to its chemical composition, indicating the presence of carbonates (carbo-) and borates (-bor-). The type locality, from which the first described specimens originated, is the saline Da Qaidam Lake in Qinghai Province, China. ## Applications Due to its rarity, small crystal size, and low hardness, carboborite has no industrial application. It is solely an object of interest for collectors specializing in rare minerals or borate minerals.

Properties

Mohs hardness: 2
Luster: Vitreous
Streak: White
Density: 2.12
Cleavage: {101}, perfect; {110}, distinct; {001}, imperfect.
Fracture: Uneven
Transparency: Translucent
Crystal system: Monoclinic

Diagnostic features

## Identification Carboborite can be identified by its habit – it forms colorless, prismatic or acicular crystals, often in radial aggregates. Key features include very low hardness (2 on the Mohs scale), vitreous luster, and perfect cleavage. It occurs in specific saline lake environments. ## Distinguishing from similar minerals It can be confused with other colorless borates or carbonates found in similar environments, such as colemanite or hydroboracite. Differentiation usually requires detailed chemical or crystallographic analysis, although carboborite is significantly softer than these. ## Crystal forms Crystals are monoclinic, with a prismatic or acicular habit. They typically occur as radial aggregates, rosettes, or chaotic clusters of fine needles.

Geological environment

## Genesis It is an evaporite mineral. It forms by precipitation from saline lake waters (brines) rich in boron, calcium, and magnesium, under arid climatic conditions. It is a product of chemical sedimentation in lake deposits. ## Mineral associations It co-occurs with other evaporite minerals, such as halite, gypsum, ulexite, hydroboracite, and pinnoite. ## Localities The most important and type locality for carboborite is the saline Da Qaidam Lake in Qinghai Province, China. This is the primary and virtually only known location from which well-formed specimens of this mineral originate.

Rarity

Very rare

For collectors

## Quality criteria Most valued by collectors are specimens with well-formed, transparent crystals forming aesthetic, radial aggregates. The absence of damage is important, which is difficult to achieve with such a soft mineral. The size of the aggregates and individual crystals also affects the value of the specimen. ## Popular localities The only source of valuable collector specimens is its type locality - the saline Da Qaidam Lake in China.

Care and storage

## Cleaning Specimens should only be cleaned very carefully, using a soft brush to remove dust. Due to its possible solubility in water, contact with it, especially with hot water or acids, should be avoided. ## What to avoid Contact with water and chemicals must be absolutely avoided. The mineral is very soft and brittle, susceptible to scratches and mechanical damage. It should be protected from high temperatures, which can cause the loss of water from its structure. ## Storage It is recommended to store specimens in a dry place, preferably in a closed display box, to protect them from moisture, dust, and damage. It should not be exposed to direct sunlight or sudden temperature changes.

External references

https://www.mindat.org/min-891.html