For which one of the following minerals, the composition given is incorrect?

• A

  $\text{ Soda ash- }\left({\mathrm{Na}}_2{\mathrm{CO}}_3\right)$

• B

  $\text{ Carnallite- }\left(\mathrm{KCl}\cdot {\mathrm{MgCl}}_2\cdot 6{\mathrm{H}}_2\mathrm{O}\right)$

• C

  $\text{ Borax- }\left({\mathrm{Na}}_2{\mathrm{B}}_4{\mathrm{O}}_7\cdot 7{\mathrm{H}}_2\mathrm{O}\right)$

• D

  $\text{ Glauber's salt-( }{\mathrm{Na}}_2{\mathrm{SO}}_4\cdot 10{\mathrm{H}}_2\mathrm{O}\text{ ) }$