igneous
Granite Cobble
Granite (Phaneritic intrusive igneous rock)
Hardness: 6-7 on Mohs scale. Color: Salt and pepper (mottled grey, white, and black). Luster: Dull to vitreous. Texture: Coarse-grained (phaneritic) crystalline structure. Cleavage: Indistinct in hand specimen. Specific Gravity: 2.63 to 2.75.
- Hardness
- 6-7 on Mohs scale
- Color
- Salt and pepper (mottled grey, white, and black)
- Luster
- Dull to vitreous
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Salt and pepper (mottled grey, white, and black). Luster: Dull to vitreous. Texture: Coarse-grained (phaneritic) crystalline structure. Cleavage: Indistinct in hand specimen. Specific Gravity: 2.63 to 2.75.
Formation & geological history
Formed from the slow cooling of silica-rich magma deep within the Earth's crust (plutonic). This specific specimen has been tumbled and rounded by water or glacial action. It can date from hundreds of millions to billions of years old.
Uses & applications
Used extensively in construction for countertops, floor tiles, and paving stones. In crushed form, used for road base and railroad ballast. Smooth river stones are used in landscaping and interior design.
Geological facts
Granite makes up a large portion of the Earth's continental crust. Mount Rushmore is carved into a massive granite batholith. It is one of the hardest and most durable common stones.
Field identification & locations
Identified by its 'salt and pepper' appearance and visible interlocking crystals of quartz, feldspar, and mica. Commonly found in riverbeds, glacial tills, and mountain ranges. Collectors look for unique mineral inclusions or weathering patterns.
