Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: tan, white, or light pink; Luster: vitreous to waxy; Crystal structure: hexagonal (internal) forming a granular texture; Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7

Formation & Geological History

Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause the sand grains and silica cement to recrystallize into an interlocking mosaic of quartz crystals. Most common in Precambrian and Paleozoic formations.

Uses & Applications

Used in construction as road ballast, gravel, and dimension stone for flooring or wall coverings. Also used industrially as a source of silica and in toolmaking historically.

Geological Facts

Quartzite is so tough and chemically resistant that it often forms the ridges of mountain ranges because it weathers much more slowly than surrounding rocks. It's often mistaken for marble but is much harder.

Field Identification & Locations

Identify by its ability to scratch glass and its grainy, crystalline appearance (sugary texture). In the field, look for smooth, rounded river cobbles like this one or massive jagged outcrops. It's found globally in fold mountain belts.

Identified on: 4/15/2026

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