igneous
Granodiorite (Water-worn Pebble)
Granodiorite
Hardness: 6-7 on Mohs scale. Color: Mottled grey, white, and black. Luster: Dull to phaneritic (crystalline). Crystal structure: Phaneritic (medium-grained intrusive). Cleavage: Varies by mineral (feldspar vs quartz). Specific gravity: 2.6-2.7.
- Hardness
- 6-7 on Mohs scale
- Color
- Mottled grey, white, and black
- Luster
- Dull to phaneritic (crystalline)
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Mottled grey, white, and black. Luster: Dull to phaneritic (crystalline). Crystal structure: Phaneritic (medium-grained intrusive). Cleavage: Varies by mineral (feldspar vs quartz). Specific gravity: 2.6-2.7.
Formation & geological history
Formed from the slow cooling of silica-rich magma beneath the Earth's surface (plutonic). This specific specimen appears water-worn, indicating erosion and transport by a river or coastline over thousands of years.
Uses & applications
Used in heavy construction, road base, as crushed stone, and occasionally for salt-and-pepper style countertops or decorative landscaping stone.
Geological facts
Granodiorite is the major component of the famous 'Stone Mountain' in Georgia and was the stone used for the Rosetta Stone. It is intermediate in composition between granite and diorite.
Field identification & locations
Identify by its 'salt and pepper' appearance and visible interlocking crystals of white/grey plagioclase feldspar and dark biotite or hornblende. Commonly found in mountain ranges and riverbeds.
