Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: typically white to gray, often with yellow or tan staining from iron oxides; Luster: vitreous to dull; Crystal structure: hexagonal (microcrystalline); Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7.

Formation & Geological History

Formed through the metamorphism of quartz-rich sandstone. Under intense heat and pressure, the individual quartz grains recrystallize and fuse together, creating a much harder rock. It is found in mountain-building regions around the world across various geological eras.

Uses & Applications

Used widely in construction as road ballast, gravel, and dimension stone. High-purity quartzite is used to produce silica sand for glassmaking and silicon for industrial electronics. It is also used for decorative kitchen countertops.

Geological Facts

Quartzite is so hard and chemically resistant that it often forms the capstones of hills and mountains because it resists erosion better than the surrounding rocks. It can be distinguished from sandstone because it breaks across the grains rather than around them.

Field Identification & Locations

Identify in the field by its extreme hardness (cannot be scratched by a steel nail) and grainy, sugary texture. It is commonly found in core areas of mountain ranges like the Appalachians or Alps. Look for a 'sparkly' appearance on fresh breaks.

Identified on: 4/14/2026

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