Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: Pink, orange, or reddish due to iron oxides; Luster: Vitreous to greasy; Crystal structure: Trigonal/Hexagonal; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.

Formation & Geological History

Formed through the metamorphism of quartz-rich sandstone. High heat and pressure cause the individual quartz grains to recrystallize and fuse together into a dense, interlocking matrix. Usually found in orogenic (mountain-building) belts.

Uses & Applications

Used as crushed stone in road construction and railway ballast. Due to its hardness and resistance to chemical weathering, it is used for countertops, floor tiles, and as a decorative stone in landscaping.

Geological Facts

Quartzite is so tough that it often outlasts the surrounding rock in mountain ranges, forming prominent peaks and ridges. It is often confused with marble, but can be distinguished because quartzite will scratch glass while marble will not.

Field Identification & Locations

Identify in the field by its sugary texture on fresh surfaces and its ability to scratch glass. It has a distinctive grainy appearance but breaks across grain boundaries. Commonly found in old mountain ranges like the Appalachians or the Scottish Highlands.

Identified on: 4/24/2026

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