The chemical formula of feldspar is:

• A

  ${\mathrm{KAlSi}}_3{\mathrm{O}}_8$

• B

  ${\mathrm{Na}}_3{\mathrm{AlF}}_6$

• C

  ${\mathrm{NaAlO}}_2$

• D

  ${\mathrm{K}}_2{\mathrm{SO}}_4\cdot {\mathrm{Al}}_2{\left({\mathrm{SO}}_4\right)}_3\cdot 4\mathrm{Al}(\mathrm{OH}{)}_3$