metamorphic

Quartzite

Quartzite (primarily SiO2)

Hardness: 7 on Mohs scale; Color: typically white, gray, or tan (may appear reddish or pinkish due to iron oxide); Luster: vitreous to dull; Crystal structure: hexagonal/trigonal (microcrystalline grains); Cleavage: none (conchoidal or irregular fracture); Specific Gravity: 2.6–2.7.

Hardness: 7 on Mohs scale
Luster: vitreous to dull

Identified January 12, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed through the regional or contact metamorphism of quartz-rich sandstone. High heat and pressure cause the original quartz sand grains and silica cement to recrystallize into a dense interlocking network of crystals. It can date from any geological age, but vast deposits are found in Precambrian shields.

Uses & applications

Extensively used in construction as crushed stone for road grit, railroad ballast, and building stone. High-purity quartzite is used in the glass industry and to produce silicon metal and ferrosilicon. It is also used in decorative landscaping and as interior countertops.

Geological facts

Quartzite is so tough that it often resists weathering better than surrounding rocks, frequently forming the caps of ridges and mountains. Unlike sandstone, which breaks around sand grains, quartzite is characterized by breaking through the grains due to the strength of the crystalline bonds.

Field identification & locations

Identify in the field by its extreme hardness (it will easily scratch glass and steel) and its granular, sugary texture. Look for smooth, conchoidal fractures across the grain. It is commonly found in fold mountain belts and areas of uplifted metamorphic basement rock globally.