Quartzite

Physical Properties

Hardness: 7 on the Mohs scale. Color: White, grey, or tan (sometimes pink or red due to iron). Luster: Vitreous to dull. Crystal structure: Hexagonal (microcrystalline). Cleavage: None, breaks with a 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, the individual quartz grains recrystallize and fuse together into a dense, interlocking network of crystals.

Uses & Applications

Used as crushed stone in road construction, as railroad ballast, and as a decorative stone in landscaping. High-purity quartzite is used to produce silica sand for glassmaking and silicon for electronics.

Geological Facts

Quartzite is so tough and resistant to chemical weathering that it often forms the ridges and peaks of mountain ranges. It is harder than steel and can easily scratch a glass plate.

Field Identification & Locations

Identify in the field by its extreme hardness (cannot be scratched by a knife) and its grainy, sandpaper-like texture that unlike sandstone, breaks through the grains rather than around them. Common in folded mountain belts like the Appalachians.

Identified on: 4/15/2026

Mode: Standard