Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: White to light grey; Luster: Vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: None (conchoidal/irregular fracture); Specific Gravity: 2.6–2.7

Formation & Geological History

Formed through the regional or contact metamorphism of quartz-rich sandstone. High heat and pressure cause the individual sand grains to recrystallize and fuse together into a dense, interlocking matrix of quartz crystals.

Uses & Applications

Used in construction as crushed stone for road grit and railway ballast. Due to its resistance to chemical weathering, it is used for countertops and floor tiles. High-purity quartzite is used to produce ferrosilicon and industrial silica sand.

Geological Facts

Quartzite is so tough that it often survives intense weathering better than the surrounding rocks, frequently forming the peaks of ridges and mountains. It is harder than steel and will easily scratch a glass plate.

Field Identification & Locations

Identify in the field by its sugary, granular texture and its inability to be scratched by a steel knife. Unlike marble, it will not fizz when exposed to dilute hydrochloric acid. It is found globally, notably in the Appalachian Mountains and the Lake Superior region.

Identified on: 4/21/2026

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