igneous
Granite Cobble
Granite (composed primarily of quartz, feldspar, and mica)
Hardness: 6-7 on Mohs scale; Color: Salt-and-pepper (white, grey, tan, and black); Luster: Dull to vitreous; Crystal structure: Phaneritic (visible interlocking grains); Specific gravity: ~2.65-2.75.
- Hardness
- 6-7 on Mohs scale
- Color
- Salt-and-pepper (white, grey, tan, and black)
- Luster
- Dull to vitreous
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Salt-and-pepper (white, grey, tan, and black); Luster: Dull to vitreous; Crystal structure: Phaneritic (visible interlocking grains); Specific gravity: ~2.65-2.75.
Formation & geological history
Formed through the slow crystallization of magma below Earth's surface. This specific specimen is a 'river rock' or cobble, meaning it has been weathered and rounded by water transport in a river or glacial environment over thousands of years.
Uses & applications
Used in construction as crushed stone, dimension stone for countertops and monuments, and for decorative landscaping.
Geological facts
Granite is the most common igneous rock found on Earth's continents. The grains are large because the magma cooled very slowly deep underground, allowing crystals to grow.
Field identification & locations
Identify by its 'salt and pepper' appearance and hardness (it cannot be scratched by a steel knife). Commonly found in riverbeds, glacial tills, and mountain outcrops.
