Borax

Formula: Na2B4O5(OH)4.8H2O hydrated borate containing hydroxyl
Specific gravity: 1.7 - 1.8
Hardness: 2 to 2½
Streak: White
Colour: White, yellowish, seldom bluish, greenish
Solubility: Soluble in water.
Melting point: 878 °C. The melt dissolves numerous metal oxides. Loses 5 mol of water when heated to 100°C, another 4 mol when heated to 150 °C, and the last mol at 400 °C. Rapidly dehydrates in air to tincalconite.
Environments:

Sedimentary environments (typical)
Volcanic sublimates and hot spring deposits

Borax is the most widespread of the borate minerals. It is formed by evaporation of enclosed lakes and as an efflorescence on the surface in arid regions. It occurs in salt lake beds, hot spring deposits and volcanic vents.