Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: White to grey, often with pink or reddish hues from iron oxide; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal; Cleavage: None/Conchoidal 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 sand grains to recrystallize and fuse into a dense, crystalline rock. Most specimens date from the Precambrian to Paleozoic eras.

Uses & Applications

Used in construction as crushed stone for road grit and railway ballast, as dimension stone for counter tops and wall coverings, and in some decorative lapidary work.

Geological Facts

Quartzite is so hard that it can scratch glass. It is much tougher than its parent rock (sandstone) because the grains have been fused together, causing it to break through the sand grains rather than around them.

Field Identification & Locations

Identify in the field by its hardness (cannot be scratched by a steel blade) and its sugary, crystalline surface texture. It is commonly found in mountain ranges and eroded river beds. Collectors look for smooth, water-worn pebbles or those with interesting mineral staining.

Identified on: 5/20/2026

Mode: Standard