Quartzite

Physical Properties

Hardness: 7 on Mohs scale. Color: Grayish-tan to brownish-pink. Luster: Vitreous to dull. Crystal structure: Hexagonal (microcrystalline). Cleavage: None (conchoidal to 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 quartz grains to recrystallize and fuse together, creating an extremely durable interlocking structure.

Uses & Applications

Used in construction as crushed stone for road ballast, as decorative building stone, and historically as a material for stone tools (lithics) due to its hardness and sharp fracture edges.

Geological Facts

Quartzite is so tough that it often survives intense weathering better than surrounding rocks, frequently forming the tops of ridges and mountains. Unlike sandstone, quartzite breaks through the quartz grains rather than around them.

Field Identification & Locations

Identify by its ability to scratch glass and its grainy, sugary texture that resembles sandstone but with fused grains. It is commonly found in folded mountain belts and ancient shield areas. Use a hardness test to distinguish from limestone.

Identified on: 5/3/2026

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