sedimentary
River Pebble (Sandstone / Quartzite)
Sedimentary rock (Quartz arenite / Quartzite pebble)
Hardness: 7 on Mohs scale (if quartzite); Color: Gray to greenish-gray; Luster: Dull to vitreous; Crystal structure: Cryptocrystalline to microcrystalline quartz grains cemented together; Cleavage: None, fractures conchoidally; Specific gravity: ~2.65.
- Hardness
- 7 on Mohs scale (if quartzite)
- Color
- Gray to greenish-gray
- Luster
- Dull to vitreous
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Physical properties
Hardness: 7 on Mohs scale (if quartzite); Color: Gray to greenish-gray; Luster: Dull to vitreous; Crystal structure: Cryptocrystalline to microcrystalline quartz grains cemented together; Cleavage: None, fractures conchoidally; Specific gravity: ~2.65.
Formation & geological history
Formed through the accumulation, compaction, and cementation of mineral particles or rock fragments over millions of years (sedimentary), often later subjected to heat and pressure (metamorphic quartzite). Rounded shape is the result of water transport and mechanical abrasion in a riverbed or coastal environment.
Uses & applications
Landscaping, decorative garden stone, construction aggregate, and educational specimens.
Geological facts
River pebbles undergo natural tumbling over vast distances, where softer minerals are worn away, leaving behind durable and weather-resistant quartz-rich rocks.
Field identification & locations
Commonly found in active or ancient riverbeds, stream channels, and alluvial terraces worldwide. To identify in the field, look for smooth, rounded edges and test hardness against a steel blade (quartzite will scratch glass).
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