Borax (mineral)
Borax (Na2B4O5(OH)4 · 8 H2O) is a borate mineral found in evaporite deposits of alkaline lacustrine environments and as a surface efflorescence in arid regions. It is the chief mineral mined from the deposits at Boron, California and nearby locations, and is the chief source of commercial borax.
| Borax | |
|---|---|
Borax from the Kramer Borate deposit, Boron, Kern Co, California, USA | |
| General | |
| Category | Nesoborate |
| Formula (repeating unit) | Na2B4O5(OH)4·8H2O |
| IMA symbol | Brx |
| Strunz classification | 6.DA.10 |
| Crystal system | Monoclinic |
| Crystal class | Prismatic (2/m) (same H-M symbol) |
| Space group | C2/c (no. 15) |
| Unit cell | a = 11.8790(2) Å, b = 10.6440(2) Å, c = 12.2012(2) Å; β = 106.617(1)°; Z = 4 |
| Identification | |
| Color | Colorless or white |
| Crystal habit | As prismatic crystals or as massive encrustations |
| Twinning | Rare on {100} |
| Cleavage | Perfect on {100}, less perfect on {100}, very poor on {010} |
| Fracture | Conchoidal |
| Mohs scale hardness | 2 to 2.5 |
| Luster | Vitreous to resinous to earthy |
| Streak | White |
| Diaphaneity | Translucent to opaque |
| Specific gravity | 1.715 |
| Optical properties | Biaxial (-) |
| Refractive index | nα = 1.4466 nβ = 1.4687 nγ = 1.4717 |
| Fusibility | 1.5 |
| Diagnostic features | Froths on heating, producing a yellow flame |
| Solubility | Soluble in water |
| References | |
Borax first reached Western civilization as tincal mined from deposits in Tibet. The term borax comes from the Arabic bauraq, meaning white.
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