igneous
Granodiorite Pebble
Granodiorite (containing Quartz, Plagioclase Feldspar, and Biotite/Amphibole)
Hardness: 6-7 on Mohs scale. Color: Salt-and-pepper (white, gray, and black). Luster: Dull to vitreous. Crystal structure: Phaneritic (medium-grained crystalline). Cleavage: Varies by mineral constituent. Specific gravity: 2.6-2.7.
- Hardness
- 6-7 on Mohs scale
- Color
- Salt-and-pepper (white, gray, and black)
- Luster
- Dull to vitreous
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Salt-and-pepper (white, gray, and black). Luster: Dull to vitreous. Crystal structure: Phaneritic (medium-grained crystalline). Cleavage: Varies by mineral constituent. Specific gravity: 2.6-2.7.
Formation & geological history
Formed from the slow cooling of silica-rich magma beneath the Earth's surface (intrusive). The rounded shape indicates secondary erosion and transport by water in a river or coastal environment.
Uses & applications
Commonly used as crushed stone for road construction, building materials, and as decorative landscaping stones. Higher quality slabs are used for countertops similarly to granite.
Geological facts
Granodiorite is the intermediate rock between granite and diorite. The famous Rosetta Stone was carved from a slab of granodiorite, though it was originally misidentified as basalt.
Field identification & locations
Identify by its 'salt and pepper' appearance and visible crystalline texture. It is harder than steel and will scratch glass. Found globally in batholiths and eroded mountain ranges, often appearing as smooth cobbles in stream beds.
