igneous
Granodiorite Pebble
Granodiorite
Hardness: 6-7 on Mohs scale. Color: Salt-and-pepper (mottled gray, white, and black). Luster: Dull to vitreous. Crystal structure: Phaneritic (visible crystals). Cleavage: Varies by mineral constituent. Specific gravity: 2.6-2.7.
- Hardness
- 6-7 on Mohs scale
- Color
- Salt-and-pepper (mottled gray, white, and black)
- Luster
- Dull to vitreous
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Salt-and-pepper (mottled gray, white, and black). Luster: Dull to vitreous. Crystal structure: Phaneritic (visible crystals). Cleavage: Varies by mineral constituent. Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the slow cooling of silica-rich magma beneath the Earth's surface (intrusive). This specific specimen is a water-worn pebble, likely eroded from a pluton and rounded by river or glacial action.
Uses & applications
Used primarily in construction as crushed stone, road base, and occasionally as decorative gravel or 'river rock' in landscaping.
Geological facts
Granodiorite is the intermediate rock between granite and diorite. The famous Rosetta Stone was carved from a slab of granodiorite, not basalt as originally thought.
Field identification & locations
Identify in the field by its phaneritic texture and the presence of more plagioclase feldspar than orthoclase. Commonly found in batholiths and mountain roots. For collectors, look for the distinct 'salt and pepper' appearance in rounded river stones.
