metamorphic
River Rock (Quartzite Pebble)
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: light grey to tan; Luster: dull to slightly vitreous; Crystal structure: granular/crystalline; Cleavage: none; Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- light grey to tan
- Luster
- dull to slightly vitreous
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Physical properties
Hardness: 7 on Mohs scale; Color: light grey to tan; Luster: dull to slightly vitreous; Crystal structure: granular/crystalline; Cleavage: none; Specific gravity: 2.6-2.7
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone under intense heat and pressure. The smoothness of this specific specimen indicates it was weathered and rounded by water action in a river or coastal environment over thousands of years.
Uses & applications
Commonly used in landscaping, as decorative aggregate in construction, and as a durable material for pathways. Higher-quality pieces are used for stone tumbling or as worry stones.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, ending up as resilient pebbles in riverbeds. It is harder than steel and will easily scratch a glass plate.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a knife) and its grainy, sugary appearance when broken. Found globally in riverbeds, beaches, and glacial till.
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