Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: typically white to gray, but can be pink or red due to iron impurities; Luster: vitreous to grainy; Crystal structure: Trigonal; Cleavage: none; Specific Gravity: 2.6 to 2.7.

Formation & Geological History

Formed when quartz-rich sandstone is subjected to intense heat and pressure (metamorphism), causing the sand grains to recrystallize and fuse together into a dense, hard rock.

Uses & Applications

Used extensively in road construction, as railroad ballast, for kitchen countertops, and as decorative stone in architecture.

Geological Facts

Quartzite is so tough that it often outlasts the surrounding rock in mountain ranges, frequently forming the tops of peaks and ridges. It is one of the hardest common rocks found on Earth's surface.

Field Identification & Locations

Identify by its extreme hardness (it will easily scratch glass) and its grainy, sugary appearance despite being very compact. It is found in mountain belts and shield areas globally.

Identified on: 4/30/2026

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