metamorphic

Weathered quartzite cobble

Quartzite (recrystallized quartz, SiO₂)

AI-generated identification · may be incorrect

Hardness about 7 Mohs; gray-brown, fine-grained, dull to subtly glassy luster, massive texture, and no obvious cleavage. The rounded shape and surface fractures indicate prolonged weathering and transport.

Identified September 17, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when quartz-rich sandstone was subjected to heat and pressure, commonly during mountain-building; its exact geological age cannot be determined from the image. The cobble was likely moved by stream, glacial, or slope processes.

Uses & applications

Used as crushed aggregate, road stone, decorative landscaping stone, and occasionally as a building or dimension stone. Attractive pieces may be collected, but this specimen appears ordinary.

Geological facts

Quartzite commonly breaks through quartz grains rather than around them, making it highly resistant to erosion. Its rusty bands likely reflect iron-oxide staining along fractures or compositional layers.

Field identification & locations

In the field, it can be distinguished from sandstone by its very hard surface and inability to scratch easily with a steel knife; quartz-rich grains often appear fused. Common in metamorphic mountain belts and derived river gravels.