igneous
Granite Cobble
Granitic intrusive igneous rock (Quartz, Feldspar, Mica)
Hardness: 6-7 on Mohs scale. Color: Mottled tan, grey, and black. Luster: Dull/earthy surface when weathered, vitreous on fresh breaks. Structure: Phaneritic (coarse-grained) crystalline texture. Specific gravity: ~2.63-2.75.
- Hardness
- 6-7 on Mohs scale
- Color
- Mottled tan, grey, and black
- Luster
- Dull/earthy surface when weathered, vitreous on fresh breaks
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Mottled tan, grey, and black. Luster: Dull/earthy surface when weathered, vitreous on fresh breaks. Structure: Phaneritic (coarse-grained) crystalline texture. Specific gravity: ~2.63-2.75.
Formation & geological history
Formed from the slow cooling of silica-rich magma deep underground. This specific specimen has been chemically weathered and physically rounded by water or glacial transport. Age can range from hundreds of millions to billions of years depending on the pluton of origin.
Uses & applications
Used primarily as construction aggregate, road base, and landscape gravel. Polished granite is used for countertops and monuments.
Geological facts
Granite makes up much of the Earth's continental crust. Because it is highly resistant to abrasion and weathering, it often survives as rounded cobbles in riverbeds long after softer rocks have eroded away.
Field identification & locations
Identify in the field by its 'salt and pepper' appearance and hardness (it will scratch glass). Commonly found in glacial till, riverbeds, and mountainous regions. It is one of the most common rocks on the planet.
