metamorphic
Rounded gray river pebble, likely quartzite or fine-grained metamorphic rock
Quartzite (probable; chiefly recrystallized quartz, SiO₂)
AI-generated identification · may be incorrectHardness about 7 Mohs; pale gray to tan, dull-to-subvitreous luster, very fine granular texture, massive structure, and no obvious cleavage. The smooth oval shape reflects prolonged water abrasion rather than crystal form.
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Physical properties
Hardness about 7 Mohs; pale gray to tan, dull-to-subvitreous luster, very fine granular texture, massive structure, and no obvious cleavage. The smooth oval shape reflects prolonged water abrasion rather than crystal form.
Formation & geological history
Likely formed when quartz-rich sandstone recrystallized under heat and pressure, commonly during regional metamorphism; its exact geologic age cannot be determined from the image. Later erosion transported and rounded it in a stream or beach environment.
Uses & applications
Primarily a decorative, landscaping, teaching, or lapidary specimen; quartzite is also used as aggregate, roadstone, dimension stone, and durable building material.
Geological facts
Quartzite commonly resists weathering better than surrounding rocks, producing rounded resistant pebbles. A glassy fracture and inability to scratch it with a steel knife support quartzite over softer sandstone.
Field identification & locations
Common in river gravels and glacial deposits worldwide, especially near exposed metamorphic belts. Confirm with a hardness test, streak (white), and acid test; the image alone cannot exclude chert, dense granite, or another gray metamorphic pebble.
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