metamorphic
Rounded river cobble, likely quartz-rich sandstone or quartzite
Indeterminate quartz-rich clastic rock; possibly quartzite (mostly SiO₂)
AI-generated identification · may be incorrectPale gray-brown, fine-grained, dull to subtly sugary luster, with rounded abrasion surfaces and a natural fracture. Likely hardness 6–7 if quartz-rich; cleavage absent and specific gravity roughly 2.6–2.7.
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Physical properties
Pale gray-brown, fine-grained, dull to subtly sugary luster, with rounded abrasion surfaces and a natural fracture. Likely hardness 6–7 if quartz-rich; cleavage absent and specific gravity roughly 2.6–2.7.
Formation & geological history
The cobble was rounded by prolonged transport in a river or beach environment. If quartzite, it began as sandstone and recrystallized during metamorphism, commonly during Precambrian–Paleozoic mountain-building; the exact age cannot be determined from the image.
Uses & applications
Commonly used as landscaping or decorative stone and occasionally as aggregate; it has little jewelry value unless unusually patterned or proven to be a distinctive quartzite.
Geological facts
The smooth shape reflects mechanical abrasion rather than crystal growth. The visible reddish-brown patches may be iron-oxide staining or minor weathered inclusions.
Field identification & locations
Identify by its dense, uniform texture, lack of visible cleavage, and inability to scratch it with a steel nail if quartz-rich; sandstone would be more granular and may shed grains. Common in stream gravels worldwide; a fresh broken surface and acid, streak, or hardness tests would improve identification.
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