Quartzite

Quartzite is a hard, nonfoliated metamorphic rock that forms from quartz-rich sandstone subjected to heat and pressure. It consists mainly of interlocking quartz grains that have recrystallized and fused together, resulting in a dense, granular texture and very high strength. The original sedimentary layers typically disappear during metamorphism, giving quartzite a uniform appearance.

Quartzite forms in convergent zones and contact metamorphic aureoles when sandstone is buried to sufficient depths or intruded by hot magma. Under elevated temperatures, quartz grains recrystallize and fuse; cementing material is redistributed, and the rock gains a durable, compact microcrystalline structure. It is typically colorless or white when pure, but iron oxide or other impurities can impart pink, red, gray, or green hues.

In terms of physical properties, quartzite has a hardness around Mohs 7, high compressive strength, and excellent abrasion resistance, making it durable for outdoor and interior use. Its nonfoliated texture means it tends to break with a conchoidal or splintery fracture rather than along planes. It is relatively chemically resistant, withstanding weathering better than many other sedimentary rocks.

Quartzite occurs widely in continental crust and is quarried for a range of purposes. Commercially important forms are used as dimension stone in exterior and interior cladding, flooring, countertops, and decorative tiles. It is also used as crushed stone for construction and as aggregate in some industrial applications.

Compared with sandstone, quartzite lacks visible sand grains and shows a uniform crystalline texture; its appearance can be strikingly uniform or variably colored depending on impurities.