igneous
River Pebble Quartzite / Granite Cobble
Quartz-rich Granitic / Quartzite Cobble
Hardness: 6-7 Mohs. Color: Yellowish-tan, grey, white with sparkly quartz grains and dark mica/amphibole flecks. Luster: Vitreous to dull, sparkling in light. Texture: Medium- to coarse-grained, rounded by river erosion.
- Hardness
- 6-7 Mohs
- Luster
- Vitreous to dull, sparkling in light
Identified More igneous →
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Physical properties
Hardness: 6-7 Mohs. Color: Yellowish-tan, grey, white with sparkly quartz grains and dark mica/amphibole flecks. Luster: Vitreous to dull, sparkling in light. Texture: Medium- to coarse-grained, rounded by river erosion.
Formation & geological history
Formed through igneous crystallization of magma or metamorphic recrystallization of sandstone, subsequently weathered, transported, and rounded by flowing water in a stream or river bed over thousands to millions of years.
Uses & applications
Used in decorative landscaping, river rock garden pathways, stream bed features, and as aggregate in construction. High durability makes it suitable for outdoor stone features.
Geological facts
Smooth river stones acquire their rounded shape from abrasion against other rocks and sediment in high-energy aquatic environments like rivers, streams, or glacial runoff channels.
Field identification & locations
Identified by its well-rounded, oblong cobble shape, visible sparkling quartz crystals, and weathered tan/grey surface. Commonly found in riverbeds, alluvial gravel deposits, and glacial tills worldwide.
