igneous
Granite Cobble
Phaneritic Felsic Igneous Rock (Granite)
Hardness: 6-7 on Mohs scale; Color: Mottled grey, pink, and black; Luster: Dull (weathered/water-worn); Crystal Structure: Prismatic/Granular; Cleavage: None (fractures unevenly); Specific Gravity: 2.6-2.7
- Hardness
- 6-7 on Mohs scale
- Color
- Mottled grey, pink, and black
- Luster
- Dull (weathered/water-worn)
Identified More igneous →
Explore Granite Cobble in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6-7 on Mohs scale; Color: Mottled grey, pink, and black; Luster: Dull (weathered/water-worn); Crystal Structure: Prismatic/Granular; Cleavage: None (fractures unevenly); Specific Gravity: 2.6-2.7
Formation & geological history
Formed from the slow crystallization of magma below Earth's surface. This specific specimen has been smoothed and rounded into a 'cobble' or 'river rock' shape through fluvial (water) or glacial erosion over thousands of years.
Uses & applications
Used primarily in landscaping, decorative masonry, and as high-quality aggregate in construction. Granite is also the source material for many kitchen countertops and architectural monuments.
Geological facts
Granite makes up a large part of the Earth's continental crust. Because it is highly resistant to weathering, these cobbles can survive long journeys in rivers or glacial till, retaining their hardness even when rounded.
Field identification & locations
Identify in the field by its 'salt and pepper' appearance and visible interlocking crystals of quartz, feldspar, and mica. This rounded shape indicates it was found in a riverbed, beach, or glacial deposit.
