What is Quartzite? Quartzite is a non-foliate metamorphic rock that is produced by the metamorphism of sandstone. It is composed primarily of quartz. Quartz is the most abundant and most common mineral on the Earth. It is found in almost every geological environment and also it is at least a component of almost every rock type. It has a hexagonal crystal structure and is made of trigonal crystallized silica. It is most varied in terms of varieties, colors and forms.