Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: typically white to gray, often with yellow or reddish staining from iron oxidation; Luster: Vitreous to waxy; Crystal Structure: Trigonal (as microcrystalline quartz); 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, original quartz grains recrystallize and fuse together into a dense, hard rock. Found in mountain belts globally.

Uses & Applications

Used in construction for road ballast, floor tiles, and countertop surfaces. Also used as a source of silica for glass manufacturing and in landscaping. Polished specimens are used as decorative stones.

Geological Facts

Quartzite is so hard that it will scratch glass and steel. It is much more durable than its parent rock (sandstone) and is often the stone forming the resistant peaks of weathered mountain ranges.

Field Identification & Locations

Identify in the field by its grainy, sugary texture and extreme hardness. Unlike marble, it will not fizz with acid. It usually breaks across the original sand grains rather than around them. Common in metamorphic terrains and as water-worn pebbles in riverbeds.

Identified on: 5/2/2026

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