Borax - Encyclopedia

    Class : Carbonates, nitrates, borates
    Subclass : Borates
    Crystal system : Monoclinic
    Chemistry : Na2B4O5(OH)4 8H2O
    Rarity : Fairly common

Borax is the most common of the borates. It is, like the majority of borates, an evaporitic mineral formed by evaporation from salt lakes in a desert environment. The waters of these lakes contain large quantities of borated brines linked to volcanic phenomena. This volcanic origin explains why borax is also, more rarely, a fumarolic product. In salt lake deposits, borax is associated with many salts : borates (ulexite, kernite, colemanite...), halite, glauberite, thenardite, gypsum... Its name comes from the Arabic buraq (white), which also designated the saltpetre of the ancient authors. It is a light mineral (density of 1.7), white or slightly tinged with yellowish, greenish, bluish or greyish. The prismatic crystals, short and often flattened, resemble those of augite. Borax is also known in compact masses. The Van der Waals bonds existing in its crystal lattice give it a low hardness (2 to 2.5). Soluble in water, it easily loses five molecules of water to turn into tincalconite : the borax crystals in the collections have thus been covered with a chalky film of this mineral. Borax is the largest source of boron on the planet, mined in the USA, Turkey and the Andean highlands. It is the commercial form of boron, with other borates being converted into borax for sale.

Borax in the World

The gigantic deposits of borates in California provide the majority of museum crystals. Giant crystals of 30 cm and enormous masses come from Boron, seat of the world's largest borate exploitation. The deposit near Borax Lake, for its part, yielded crystals 15 cm in diameter, Death Valley and Searles Lake crystals of similar quality. We should also mention the Kirka deposit (Turkey) and, for their historical role, the Tibetan deposits of Rudok and Ladakh, pioneers in the industrial use of borax.

Borax in France

Borax is not present in the French subsoil.


A twin on {100} exists but is rare.

Fakes and scams

No fake inventories for this mineral species.

Hardness : 2 to 2.5
Density : 1.71
Fracture : Conchoidal
Trace : White

TP : Translucent to opaque
RI : 1.447 to 1.472
Birefringence : 0.025
Optical character : Biaxial -
Pleochroism : None
Fluorescence : Blue-green

Solubility : Water

Magnetism : None
Radioactivity : None