Quartzite (River Stone)

Physical Properties

Hardness: 7 (Mohs scale); Color: Grayish-blue with white/rusty veins; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Specific gravity: 2.6 - 2.8; Cleavage: None/Conchoidal fracture.

Formation & Geological History

Formed through the metamorphism of quartz sandstone under high heat and pressure. This specific specimen has been further shaped into a rounded pebble by fluvial (river) or glacial transport, which smoothed its edges over thousands of years.

Uses & Applications

Used as aggregate in construction, as a ballast in railways, as high-purity silica for manufacturing, and often as decorative landscaping stone.

Geological Facts

Quartzite is so hard that it can scratch steel and glass. It is often more durable than the mountains it originated from, which is why it frequently survives as rounded pebbles in creek beds long after softer rocks have eroded away.

Field Identification & Locations

Identify by its extreme hardness and grainy, sugary texture under a lens. It will not bubble with acid (distinguishing it from limestone). Commonly found in riverbeds, glacial tills, and mountainous regions worldwide.

Identified on: 4/18/2026

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