Hydroboracite is a hydrated borate mineral (hence the name) of calcium and magnesium, whose chemical composition is CaMgB6O8(OH)6·3H2O. It is a minor borate ore mineral. It is a mineral consisting of a white hydrous calcium magnesium borate and occurring in fibrous and foliated masses. Ulexite is another more common borate that forms similar fibrous aggregates and thus the two minerals are not easy to distinguish. It was discovered in 1834 in Atyrau Province, Kazakhstan.
- Category: Inoborates
- Formula: CaMgB6O8(OH)63H2O
- Crystal system: Monoclinic
- Crystal class: Prismatic (2/m) (same H-M symbol)
Hydroboracite is an uncommon borate mineral. It is one of the borate minerals that form silky, fibrous crystal clusters. Hydroboracite’s silky luster is quite attractive.
- Color: Colorless, white
- Mohs scale hardness: 2
- Luster: Vitreous, silky
- Diaphaneity: Transparent
- Density: 2
- Habit: Fibrous – Crystals made up of fibers.
- Hardness: 2 – Gypsum
- Luminescence: Non-fluorescent.
- Streak: white
- Optical properties: Biaxial (+)
Occurrence: Typically formed by groundwater alteration of colemanite; may be primary.
Association: Colemanite, hydroboracite, tunellite.