Borax is prepared by treating colemanite with

Borax is prepared when colemanite reacts with sodium carbonate.

$\underset{\mathrm{Colemanite}}{{\mathrm{Ca}}_2{\mathrm{B}}_6{\mathrm{O}}_{11}}+2{\mathrm{Na}}_2{\mathrm{CO}}_3⟶2{\mathrm{CaCO}}_3\downarrow +\underset{\mathrm{Borax}}{{\mathrm{Na}}_2{\mathrm{B}}_4{\mathrm{O}}_7}+2{\mathrm{NaBO}}_2$