igneous
Granite Cobble
Granite (Felsic Plutonic Rock)
Hardness: 6-7 Mohs; Color: Light gray, tan, or pink with visible multicolored grains; Luster: Dull (weathered) to vitreous (fresh surfaces); Crystal Structure: Phaneritic (coarse-grained crystals); Specific Gravity: 2.63-2.75.
- Hardness
- 6-7 Mohs
- Color
- Light gray, tan, or pink with visible multicolored grains
- Luster
- Dull (weathered) to vitreous (fresh surfaces)
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Physical properties
Hardness: 6-7 Mohs; Color: Light gray, tan, or pink with visible multicolored grains; Luster: Dull (weathered) to vitreous (fresh surfaces); Crystal Structure: Phaneritic (coarse-grained crystals); Specific Gravity: 2.63-2.75.
Formation & geological history
Formed through the slow crystallization of silica-rich magma beneath the Earth's surface. This specific specimen is a 'glacial cobble' or 'river rock,' rounded by high-energy water transport or glacial movement over thousands to millions of years.
Uses & applications
Used widely in construction as crushed stone, dimension stone for countertops and monuments, and as a decorative landscaping element.
Geological facts
Granite makes up a large portion of the Earth's continental crust. Because it is very hard and resistant to weathering, it often survives as rounded boulders in riverbeds long after softer rocks have eroded away.
Field identification & locations
Identify by its 'salt and pepper' appearance caused by interlocking crystals of quartz (clear/white), feldspar (opaque white/pink), and mica (black). Commonly found in glaciated regions or mountain streams.
