Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: White to light grey; Luster: Vitreous to dull; Crystal structure: Trigonal (granular); Cleavage: None, exhibits conchoidal fracture; Specific gravity: 2.6-2.7.

Formation & Geological History

Formed from the regional or contact metamorphism of quartz-rich sandstone. High heat and pressure cause the sand grains to recrystallize and fuse together into a dense, hard rock.

Uses & Applications

Used extensively in road construction, as railway ballast, for making silica glass, and as decorative stone for countertops or landscaping. High-purity quartzite is used in the metallurgical industry.

Geological Facts

Quartzite is so tough that it often outlasts the surrounding rock in weathering processes, frequently forming the tops of ridges and resistant hills called hogbacks.

Field Identification & Locations

Identify by its high hardness (it will scratch glass) and lack of reaction to acid. It appears more 'sugary' than marble and breaks across the grains rather than around them. Found globally in ancient tectonic belts and mountain ranges.

Identified on: 5/16/2026

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