igneous
Granite Cobble
Granite (Phaneritic Quartz-Feldspar-Mica intrusive rock)
Hardness: 6-7 (Mohs). Color: Salt-and-pepper (white/grey with black specks). Luster: Dull (weathered) to vitreous (on fresh surface). Structure: Medium-grained phaneritic. Specific Gravity: 2.63 - 2.75.
- Hardness
- 6-7 (Mohs)
- Color
- Salt-and-pepper (white/grey with black specks)
- Luster
- Dull (weathered) to vitreous (on fresh surface)
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Physical properties
Hardness: 6-7 (Mohs). Color: Salt-and-pepper (white/grey with black specks). Luster: Dull (weathered) to vitreous (on fresh surface). Structure: Medium-grained phaneritic. Specific Gravity: 2.63 - 2.75.
Formation & geological history
Formed from the slow cooling of silica-rich magma deep underground (plutonic). This specimen has been rounded by fluvial or coastal erosion, likely over thousands of years.
Uses & applications
Construction material, dimension stone, landscaping, and aggregate. In this small, rounded form, it is used for decorative gardens or as worry stones.
Geological facts
Granite makes up a large portion of the Earth's continental crust. Because of its hardness and resistance to erosion, it often persists as rounded cobbles long after softer rocks have broken down into sand.
Field identification & locations
Identify in the field by its 'salt and pepper' appearance and visible interlocking crystals of quartz, feldspar, and biotite. Found globally in riverbeds, glacial tills, and beaches.
