metamorphic
River Pebble (Gneiss / Granitic Schist)
Metamorphic Rock (Quartz-Feldspar-Mica assembly)
Hardness: 6-7 on Mohs scale; Color: Mottled gray, tan, brown, and off-white; Luster: Dull to slightly sparkling from mica flakes; Texture: Medium to coarse-grained, rounded and smoothed by water erosion; Cleavage: None (massive to weakly foliated).
- Hardness
- 6-7 on Mohs scale
- Color
- Mottled gray, tan, brown, and off-white
- Luster
- Dull to slightly sparkling from mica flakes
Identified More metamorphic →
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Mottled gray, tan, brown, and off-white; Luster: Dull to slightly sparkling from mica flakes; Texture: Medium to coarse-grained, rounded and smoothed by water erosion; Cleavage: None (massive to weakly foliated).
Formation & geological history
Formed via regional metamorphism of pre-existing sedimentary or igneous rocks deep under high temperature and pressure. Later eroded out of bedrock and naturally rounded by stream or river water transport over hundreds to thousands of years.
Uses & applications
Used primarily in landscaping, garden decoration, aquarium substrates, aggregate in concrete, and as decorative stone paths.
Geological facts
Smooth river pebbles owe their rounded shapes entirely to fluid dynamics and physical attrition as they collide with other stones in moving water over long periods.
Field identification & locations
Identified by its well-rounded, egg-like shape, smooth texture, and visible interlocking mineral grains (quartz, feldspar, and dark biotite/amphibole). Extremely common along riverbeds, beaches, and glacial till deposits worldwide.
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