metamorphic
River Pebble (Gneiss or Quartzite)
Metamorphic rock specimen (likely Gneiss or impure Quartzite)
Hardness 6-7 (Mohs), colors include gray and tan with visible banding, dull to earthy luster when dry, dense/fine-grained texture, smooth rounded surface from water erosion.
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Physical properties
Hardness 6-7 (Mohs), colors include gray and tan with visible banding, dull to earthy luster when dry, dense/fine-grained texture, smooth rounded surface from water erosion.
Formation & geological history
Formed through high-pressure and high-temperature metamorphism of pre-existing rocks (protoliths). This specimen has been significantly smoothed and rounded by transport in a river or creek bed over hundreds to thousands of years.
Uses & applications
Common river stones are used in landscaping, as aquarium decor, or as decorative filler in construction. Small pebbles like this have high educational value for amateur geologists.
Geological facts
The rounded shape of river stones is a result of fluvial erosion, where individual rocks collide and grind against each other in moving water, a process known as 'attrition'.
Field identification & locations
Identify by its smooth, oval shape and hard surface that cannot be scratched by a steel knife. Commonly found in active or ancient riverbeds and glacial deposits. Look for alternating light and dark bands indicating metamorphic origin.
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