Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: white to light gray; Luster: vitreous or sugary (saccharoidal); Crystal structure: trigonal (microcrystalline); Fracture: conchoidal or irregular; Density: ~2.65 g/cm3.

Formation & Geological History

Formed through the metamorphism of quartz-rich sandstone. Under intense heat and pressure, original quartz grains recrystallize and fuse together into a dense, hard rock. Typically associated with regional metamorphism in mountain-building zones.

Uses & Applications

Used as crushed stone in road construction, railroad ballast, and as a raw material for glass making and silica production. Polished slabs are used for countertops and flooring due to its extreme durability and resistance to chemicals.

Geological Facts

Quartzite is so tough that it often survives intense erosion cycles that wear away surrounding rocks, frequently forming the caps of high mountain ridges and hills known as monadnocks.

Field Identification & Locations

Identify in the field by its inability to be scratched by a steel knife (hardness) and its tendency to break through quartz grains rather than around them (unlike sandstone). Commonly found in Precambrian shields and eroded mountain ranges globally.

Identified on: 4/30/2026

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