Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: Tan, gray, or white; Luster: Vitreous to dull; Crystal structure: Non-foliated, interlocking quartz grains; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Formation & Geological History

Formed from the metamorphism of quartzose sandstone under high heat and pressure, typically during mountain-building events (orogeny). The original quartz grains recrystallize into a dense, interlocking mosaic.

Uses & Applications

Used as crushed stone for road construction, railway ballast, and as a decorative stone in landscaping. High-purity quartzite is used to produce silica sand for glassmaking and industrial abrasives.

Geological Facts

Quartzite is so tough that it usually breaks through the quartz grains rather than along the boundaries between them, unlike its parent rock, sandstone. It is often one of the most resistant rocks to weathering, frequently forming the tops of ridges and mountains.

Field Identification & Locations

Identify in the field by its extreme hardness (it will easily scratch glass) and lack of foliation. It often has a crystalline, 'sugar-like' appearance on fresh surfaces. This water-worn specimen shows a smooth, rounded river-tumble texture.

Identified on: 4/19/2026

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