Quartzite River Rock

Physical Properties

Hardness: 7 on Mohs scale; Color: Off-white to light gray with slight tan staining; Luster: Dull to vitreous; Crystal structure: Non-foliated, interlocking quartz grains; Cleavage: None; Specific gravity: 2.6-2.7

Formation & Geological History

Formed from the metamorphism of quartz sandstone under high heat and pressure. This specific specimen has been further shaped by fluvial erosion (river water), creating its smooth, egg-like ellipsoidal shape over thousands of years.

Uses & Applications

Commonly used in landscaping (decorative river stones), construction aggregate, and as high-silica raw material for glass making. Tumbled specimens are popular with hobbyists for rock painting.

Geological Facts

Quartzite is so tough that it often outlasts the surrounding rock, which is why it is frequently found as rounded cobbles in riverbeds. It is harder than steel and will easily scratch a glass plate.

Field Identification & Locations

Identify in the field by its extreme hardness and grainy, sugary texture under a hand lens. It lacks the reactiveness to acid that marble has. They are ubiquitous in glaciated regions and river basins globally.

Identified on: 4/13/2026

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