metamorphic

Quartzite (River Cobble)

Metamorphic Quartz-rich Rock

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale), Color: Tan to reddish-brown (likely due to iron oxide staining), Luster: Dull/waxy when weathered, Crystal structure: Granoblastic (microcrystalline), Cleavage: None (conchoidal fracture)

Identified May 12, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed from the metamorphism of quartz-rich sandstone under high heat and pressure. This specific specimen shows rounding and smoothing from transport in a river or stream environment.

Uses & applications

Used extensively in construction as crushed stone or ballast, and as a raw material for glass and ceramics if high purity; also used as landscaping rock.

Geological facts

Quartzite is one of the most durable and weather-resistant rocks on Earth. This piece likely contains iron impurities that give it its brownish hue, a process known as iron-oxide staining.

Field identification & locations

Identify in the field by its inability to be scratched by a steel nail, its granular texture (like sandpaper frozen in glass), and lack of fizzing when exposed to acid. Commonly found in riverbeds and mountainous regions.