Answer:
None
Step-by-step explanation:
Quartz is a silicate mineral. It is made up of interlocking chain of silica that forms a framework pattern. Pure quartz is made up of silica and silica alone. Silica has a formula of SiO₂. Quartz is pure silica.
Fe and Mg are not in the framework of silica. They even rarely occur as impurities in the structure of the mineral.