Kieselguhr, an amorphous form of silica is used in filtration plants.
Quartz is one of the most common minerals in the earth’s crust having a specific crystalline form.
Cristobalite is a high temperature polymorph of silica, having same chemical formula as quartz but distinct crystal structure.
Tridymite is also a high temperature polymorph of silica and occurs as hexagonal crystals.