igneous
Granite (River Pebble)
Phaneritic Felsic Igneous Rock
Hardness: 6-7 Mohs; Color: Salt-and-pepper (gray, white, black); Luster: Dull to vitreous; Crystal Structure: Phaneritic (visible interlocking crystals of quartz, feldspar, and biotite/amphibole); Specific Gravity: 2.63-2.75.
- Hardness
- 6-7 Mohs
- Color
- Salt-and-pepper (gray, white, black)
- Luster
- Dull to vitreous
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Physical properties
Hardness: 6-7 Mohs; Color: Salt-and-pepper (gray, white, black); Luster: Dull to vitreous; Crystal Structure: Phaneritic (visible interlocking crystals of quartz, feldspar, and biotite/amphibole); Specific Gravity: 2.63-2.75.
Formation & geological history
Formed from the slow cooling of silica-rich magma deep underground (plutonic). This specific specimen is a water-worn river pebble, likely rounded by fluvial erosion over thousands of years.
Uses & applications
Used widely in construction (countertops, flooring), crushed stone for roads, and as decorative landscaping stones and polished river rocks.
Geological facts
Granite makes up a large portion of the Earth's continental crust. It is extremely durable, which is why ancient civilizations used it for monuments like the Great Pyramid of Giza's King's Chamber.
Field identification & locations
Identify by the 'salt and pepper' appearance of interlocking light and dark crystals and its extreme hardness (cannot be scratched by a steel knife). Commonly found in riverbeds, glacial tills, and mountain ranges.
