Water of crystallization in Borax? 

Borax is a natural mineral and a hydrated salt of boric acid. It is also known as sodium borate decahydrate or sodium tetraborate decahydrate $({\mathrm{Na}}_2{\mathrm{B}}_4{\mathrm{O}}_7.10{\mathrm{H}}_2\mathrm{O}).$ It is a powdery white substance widely used as a household cleaner and a booster for laundry detergent. Borax is manufactured from sodium carbonate.