Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: Gray, white, or yellowish-tan; Luster: Vitreous to dull; Crystal structure: Hexagonal (as quartz grains); Cleavage: None; Specific gravity: 2.6 - 2.7

Formation & Geological History

Formed through the metamorphism of quartz sandstone under high heat and pressure. This process causes the individual quartz grains to recrystallize and fuse into a dense, interlocking matrix.

Uses & Applications

Used in construction as road ballast, gravel, and building stone. High-purity quartzite is used to produce silica sand for glassmaking and silicon for electronics. Also used as decorative stone in landscaping.

Geological Facts

Quartzite is so tough that it often outlasts the surrounding rocks during erosion, frequently forming the peaks of ridges and mountains. It is harder than a steel knife and will easily scratch glass.

Field Identification & Locations

Identify in the field by its extreme hardness and its sugary, granular texture. Unlike sandstone, it will break through the quartz grains rather than around them. Common in mountainous regions and ancient metamorphic shields.

Identified on: 4/29/2026

Mode: Standard