Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: typically white to gray, often with brownish or reddish staining; Luster: vitreous to dull; Crystal structure: Trigonal (as quartz grains); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.

Formation & Geological History

Formed through the metamorphism of quartz sandstone. Intense heat and pressure cause the original quartz grains to recrystallize and fuse together into a dense, hard rock. This specimen appears to be a water-worn or weathered fragment found in a fluvial or glacial environment.

Uses & Applications

Used as crushed stone in road construction, as railway ballast, and in the production of glass and industrial silica. High-quality slabs are used for countertops and floor tiles.

Geological Facts

Quartzite is so hard and chemically resistant that it often forms the caprock or ridges of mountain ranges because it resists erosion better than the surrounding rocks. It can easily be mistaken for marble, but unlike marble, it will not fizz in acid and is hard enough to scratch glass.

Field Identification & Locations

Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and its grainy, sugary texture where it is broken. It is found globally in metamorphic belts. Collectors look for pieces with unique inclusions or interesting staining.

Identified on: 4/19/2026

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