metamorphic
River Pebble (Likely Quartzite or Gneiss)
Metamorphosed Silicate Rock (primarily SiO2)
Hardness: 6.5–7 on Mohs scale; Color: Mottled grey, tan, and cream; Luster: Dull to waxy when dry; Structure: Crystalline/Massive (rounded by abrasion); Specific gravity: ~2.65.
- Hardness
- 6
- Color
- Mottled grey, tan, and cream
- Luster
- Dull to waxy when dry
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Physical properties
Hardness: 6.5–7 on Mohs scale; Color: Mottled grey, tan, and cream; Luster: Dull to waxy when dry; Structure: Crystalline/Massive (rounded by abrasion); Specific gravity: ~2.65.
Formation & geological history
Formed through the intense heat and pressure of burial (regional metamorphism) of sandstone or granite; later weathered out of parent rock and rounded by transport in a river or glacial environment over thousands of years.
Uses & applications
Common river stones are used broadly in landscaping, as decorative aggregate in construction, and occasionally for lapidary tumbling for beginners.
Geological facts
This specimen is a well-rounded 'clast.' Its smooth, egg-like shape is a result of millions of collisions with other rocks in a high-energy water environment, a process known as saltation.
Field identification & locations
Identify in the field by its smooth, water-worn exterior and lack of sharp edges. These are found in active or ancient riverbeds, beaches, and glacial till. Scratch with a steel file to check hardness; it should resist most steel.
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