igneous
River Rock (Granite Cobble)
Granite (Phaneritic Quartz-Feldspar-Mica intrusive rock)
Hardness: 6-7 Mohs; Color: Salt and pepper (gray, white, black, tan); Luster: Dull to vitreous; Crystal structure: Phaneritic (visible crystals); Cleavage: None (irregular fracture); Specific Gravity: 2.63 - 2.75
- Hardness
- 6-7 Mohs
- Color
- Salt and pepper (gray, white, black, tan)
- Luster
- Dull to vitreous
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Physical properties
Hardness: 6-7 Mohs; Color: Salt and pepper (gray, white, black, tan); Luster: Dull to vitreous; Crystal structure: Phaneritic (visible crystals); Cleavage: None (irregular fracture); Specific Gravity: 2.63 - 2.75
Formation & geological history
Formed from the slow cooling of silica-rich magma deep underground, creating an intrusive igneous body. This specimen has been smoothed and rounded over thousands of years by water erosion in a river or glacial environment.
Uses & applications
Construction aggregate, landscaping, architectural stone, and occasionally used as a decorative garden element or for stone masonry.
Geological facts
Granite makes up much of the Earth's continental crust. Because it is so hard and durable, ancient civilizations like the Egyptians used it for obelisks and pyramids. River-worn granite like this is often used in Zen gardens to represent the flow of water.
Field identification & locations
Identify by its interlocking granular texture of quartz (clear/gray) and feldspar (white/pink) with dark mica flakes. Found in mountainous or glaciated regions and riverbeds. It will not react with acid, unlike limestone.
