igneous
Granite River Cobble
Phaneritic Felsic Igneous Rock (Granite)
Hardness: 6-7 Mohs; Color: Light gray to whitish with salt-and-pepper flecks; Luster: Dull (weathered) to vitreous (on fresh surfaces); Crystal Structure: Phaneritic (visible grains of quartz, feldspar, and mica); Specific Gravity: 2.6-2.7.
- Hardness
- 6-7 Mohs
- Color
- Light gray to whitish with salt-and-pepper flecks
- Luster
- Dull (weathered) to vitreous (on fresh surfaces)
Identified More igneous →
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Physical properties
Hardness: 6-7 Mohs; Color: Light gray to whitish with salt-and-pepper flecks; Luster: Dull (weathered) to vitreous (on fresh surfaces); Crystal Structure: Phaneritic (visible grains of quartz, feldspar, and mica); Specific Gravity: 2.6-2.7.
Formation & geological history
Formed from the slow cooling of silica-rich magma deep underground, typically during the Precambrian to Cenozoic eras. This specific specimen has been rounded by fluvial processes (river or stream water erosion) over thousands of years.
Uses & applications
Used extensively in landscaping, river restoration projects, construction aggregate, and as decorative garden stones. Larger deposits are quarried for dimension stone.
Geological facts
Granite makes up the majority of the Earth's continental crust. Its durability against weathering makes it the primary material for most rounded river rocks found in temperate regions.
Field identification & locations
Identify by the 'salt and pepper' appearance of interlocking crystals and its extreme hardness. It won't be scratched by a steel knife. Commonly found in glacial till, riverbeds, and mountain streams.
