metamorphic

Rounded quartz-rich cobble, likely quartzite or weathered sandstone

Quartzite (mostly SiO₂), possibly ferruginous quartz sandstone

AI-generated identification · may be incorrect

Hardness about 6.5–7 if quartzite; tan-gray, fine-grained, dull to subtly sparkly, with dark iron-oxide seams and no obvious cleavage. The rounded shape indicates natural water abrasion or prolonged weathering.

Identified September 12, 2026More metamorphic →

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Physical properties

Formation & geological history

Likely formed from quartz sand cemented into sandstone, then possibly metamorphosed into quartzite; the rock’s original age cannot be determined from the image. It was later transported and rounded in a river, beach, or glacial deposit.

Uses & applications

Usually used as a decorative or landscaping stone, aggregate, or lapidary specimen; quality quartzite can be cut for countertops and building stone. This individual cobble has little commercial value.

Geological facts

Quartz-rich rocks commonly resist weathering while softer minerals erode away, producing durable rounded cobbles. Dark lines may be iron staining, fractures, or thin mineral veins.

Field identification & locations

Scratch-testing glass and checking for sand-sized grains can help distinguish quartzite from sandstone; quartzite breaks across grains, whereas sandstone often crumbles along grain boundaries. Common in river gravels and glacial deposits worldwide.