Quartzite (River Stone)

Physical Properties

Hardness: 7 (Mohs scale); Color: Grayish-brown; Luster: Dull to vitreous when wet; Crystal structure: Non-foliated, granular; Cleavage: None; Specific gravity: 2.6-2.7. Highly durable and resistant to scratching.

Formation & Geological History

Formed through the metamorphism of quartz-rich sandstone subjected to extreme heat and pressure. This specific grain-rounded shape indicates it was polished by water in a river or coastal environment.

Uses & Applications

Commonly used in landscaping, as construction aggregate, for railroad ballast, and occasionally for primitive tools due to its hardness.

Geological Facts

Quartzite is so hard that it can scratch glass and steel easily. It is often mistake for marble, but marble will react with acid and quartzite will not.

Field Identification & Locations

Identify in the field by its grainy, sandpaper-like texture (even when smooth) and its inability to be scratched by a steel knife. Found globally in riverbeds and mountainous glaciated regions.

Identified on: 5/1/2026

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