igneous
Weathered quartz-rich river cobble
Likely granitic or quartzitic rock; exact identification is uncertain from the photograph
AI-generated identification · may be incorrectRounded by stream transport, with rusty brown iron-oxide staining, white/gray quartz or feldspar patches, and a dull granular surface. Likely hardness about 6–7 Mohs, nonmetallic luster, massive texture, and no obvious cleavage.
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Physical properties
Rounded by stream transport, with rusty brown iron-oxide staining, white/gray quartz or feldspar patches, and a dull granular surface. Likely hardness about 6–7 Mohs, nonmetallic luster, massive texture, and no obvious cleavage.
Formation & geological history
Probably eroded from a nearby igneous or metamorphic bedrock source and rounded in a river or gravel deposit; its original rock may be Precambrian to younger depending on locality. Brown coloration comes from weathering of iron-bearing minerals.
Uses & applications
Commonly used as decorative landscaping stone, aquarium or craft material, and aggregate; little jewelry value unless cutting reveals attractive quartz patterns.
Geological facts
The smooth shape indicates prolonged abrasion in moving water rather than glacial or freshly broken origin. The orange-brown coating is typically limonite/goethite, not the primary rock color.
Field identification & locations
Look for visible interlocking quartz and feldspar grains to support granite, or a uniformly sugary quartz texture to support quartzite; a streak, acid test, and fresh broken surface would improve identification. Common in riverbeds worldwide.
