quartzites

Quartzite is a non-foliated metamorphic rock formed from quartz-rich sandstone (usually quartz arenite) through the metamorphic recrystallization of quartz grains under heat and pressure. The original sedimentary textures are largely obliterated as grains fuse together to form an interlocking mosaic of quartz crystals.

Formation occurs during regional or contact metamorphism, with temperatures typically above 200–500°C and sufficient pressure to drive recrystallization and cement dissolution. The silica cement dissolves and re-precipitates as interlocking quartz, yielding a very hard, dense rock.

Composition and texture: quartzite is composed mainly of quartz with minor impurities such as iron oxides, feldspar, or mica that influence color. It is usually white to gray, but pink, red, yellow, or green tones can occur depending on impurities. It has a Mohs hardness around 7 and a granular to sugary appearance; the grains interlock, giving high strength and abrasion resistance. It is generally low in porosity and highly resistant to weathering, though it may fracture along joints or planes related to original bedding or metamorphic textures.

Uses and occurrence: quartzite occurs in many continental crust regions and is widely used as a durable construction and decorative stone. It is employed as dimension stone, paving, facing stone, and in tiles and countertops, as well as in some cases for road aggregates, due to its hardness and resistance to weathering.

Relation to related rocks: quartzite forms from quartz-rich sandstone through metamorphism and is distinct from ordinary sandstone and from foliated metamorphic rocks such as slate, phyllite, or schist.