Quartzite is a metamorphic rock which is mainly composed of quartz and usually forms from the regional metamorphism of sandstones. Quartzite is grey to white in colour and is extremely hard due to the pressure dissolution of adjacent quartz grains incurred during metamorphism.

The Dalradian Supergroup of metamorphic rocks on Arran contains quartzites. These occur as homogeneous layers which are interbedded with pelitic and psammitic schists and slates.