Hexahydroborite
Chemical formula: Ca[B(OH)<sub>4</sub>]<sub>2</sub>·2H<sub>2</sub>O
Hexahydroborite is a rare, colorless or white calcium borate, forming small, acicular crystals in borate deposits.
Properties
- Mohs hardness
- 2.5
- Luster
- Vitreous, Pearly
- Streak
- White
- Density
- 1.88
- Cleavage
- Perfect on {010}, good on {100}
- Fracture
- Uneven
- Transparency
- Transparent to translucent
- Crystal system
- Monoclinic
Diagnostic features
## Identification Hexahydroborite is difficult to identify visually. It usually forms white, earthy, or chalky coatings and aggregates. Small, acicular crystals visible under magnification can be a clue. Solubility in water and acids is a characteristic feature. Definitive identification requires advanced analytical methods, such as X-ray diffraction (XRD). ## Distinguishing from Similar Minerals It can be confused with other secondary borates, such as colemanite, ulexite, or hydroboracite, which often co-occur in the same environment. Distinguishing them based on visual characteristics is practically impossible and requires chemical or crystallographic analysis. ## Crystal Forms It forms small, elongated, acicular crystals with a rectangular cross-section. These crystals often combine into radial or fibrous aggregates, as well as spherulitic clusters.
Geological environment
## Genesis Hexahydroborite is a secondary mineral, formed as a result of weathering or alteration processes of other borate minerals in the oxidation zones of boron deposits. It forms under low-temperature conditions in an environment rich in calcium and boron, typical of evaporites (salt deposits). ## Mineral Associations It most commonly co-occurs with other borate minerals, such as hydroboracite, colemanite, inyoite, inderborite, as well as gypsum and calcite. ## Localities The most important and best-documented occurrences of this mineral are in Kazakhstan, in the Atyrau region (Inder B-Mo-Sr deposit). It has also been described from other localities worldwide where borate deposits occur, including Death Valley in California (USA) and Turkey.
Rarity
Rare
For collectors
## Quality Criteria For collectors, the most valuable specimens are those with well-formed crystals visible under magnification, forming aesthetic, radial aggregates. Due to the rarity of the mineral, any well-documented specimen, even in the form of microcrystals, has collector's value. A contrasting matrix or association with other rare borates increases the attractiveness of the specimen.
Care and storage
## Cleaning Specimens should only be dry-cleaned, using a soft brush to remove dust. Contact with water, especially warm water, can lead to dissolution or damage to the mineral. ## What to Avoid Avoid all contact with water and other liquids. The mineral is sensitive to changes in humidity and temperature. It should not be heated or exposed to acids, which decompose it. Due to its low hardness, it is very susceptible to mechanical damage. ## Storage It is recommended to store specimens in sealed, dry containers (e.g., "membrane box" type or in boxes with a desiccant). They should be protected from dust, moisture, and mechanical damage.