Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: typically white, gray, or yellowish as seen here; Luster: Vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Formation & Geological History

Formed through the regional or contact metamorphism of quartz-rich sandstone under intense heat and pressure, causing the sand grains to recrystallize into an interlocking mosaic.

Uses & Applications

Used primarily in construction for road ballast, floor tiles, and roofing. Higher quality specimens are used for decorative purposes, countertops, and as a source of silica in glass manufacturing.

Geological Facts

Quartzite is so tough that it often outlasts the surrounding rocks in mountainous areas, forming the sharp caps of ridges. It is often confused with marble but can be distinguished because quartzite will scratch glass while marble will not.

Field Identification & Locations

Identify in the field by its extreme hardness and its sugary, granular texture. It will not fizz with acid, unlike marble or limestone. Commonly found in folded mountain belts globally, such as the Appalachians or the Alps.

Identified on: 4/20/2026

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