Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: Grayish-white with dark inclusions; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal (granular texture); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Formation & Geological History

Formed from the metamorphism of quartz-rich sandstone under intense heat and pressure, typically during mountain-building events. Geological age varies by location, often Precambrian or Paleozoic.

Uses & Applications

Used in construction as crushed stone for roadbeds, as a decorative stone in landscaping, in glass manufacturing if pure enough, and frequently used for tool-making by prehistoric humans.

Geological Facts

Quartzite is so hard and chemically resistant that it often forms the resistant caps of ridges and mountains. It is harder than a steel knife and will easily scratch glass.

Field Identification & Locations

Identify by its extreme hardness and the way it breaks through the quartz grains rather than around them (unlike sandstone). Commonly found in folded mountain belts globally.

Identified on: 5/10/2026

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