Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: Grayish-white with some iron staining; Luster: Vitreous to dull; Crystal structure: Non-foliated, granular; Cleavage: None (conchoidal fracture).

Formation & Geological History

Formed through the metamorphism of quartz sandstone. High heat and pressure in regional metamorphic environments cause the individual quartz grains to recrystallize and fuse together. Often found in mountain belts and Precambrian shields.

Uses & Applications

Used extensively in construction as road ballast, gravel, and dimension stone. High-purity quartzite is used to produce ferrosilicon, industrial silica sand, and glass. High-quality slabs are used for kitchen countertops.

Geological Facts

Quartzite is so strong that when it breaks, it breaks through the quartz grains rather than along the boundaries between them, a key distinction from its parent rock, sandstone. It is highly resistant to chemical weathering.

Field Identification & Locations

Identify in the field by its extreme hardness (cannot be scratched by steel) and lack of reaction to acid. Look for a sugary texture on fresh surfaces. Common in mountain regions like the Appalachians or the Alps.

Identified on: 5/15/2026

Mode: Standard