igneous
Granodiorite
Granodiorite (Intermediate intrusive igneous rock)
Hardness: 6-7 on Mohs scale. Color: Salt-and-pepper (white, grey, and black). Luster: Phaneritic (crystalline). Crystal structure: Coarse-grained intrusive. Cleavage: Indistinct. Specific gravity: 2.6-2.7.
- Hardness
- 6-7 on Mohs scale
- Color
- Salt-and-pepper (white, grey, and black)
- Luster
- Phaneritic (crystalline)
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Salt-and-pepper (white, grey, and black). Luster: Phaneritic (crystalline). Crystal structure: Coarse-grained intrusive. Cleavage: Indistinct. Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the slow cooling of silica-rich magma beneath the Earth's surface (plutonic). While the Boones County/Northern Kentucky region is primarily sedimentary (Ordovician limestone), this specimen was likely transported via glacial till during the Pleistocene ice ages or brought in as landscaping gravel/riprap.
Uses & applications
Used extensively in construction as crushed stone, road fill, and dimension stone for countertops and monuments. Highly valued for durability.
Geological facts
Granodiorite is the main component of the Sierra Nevada batholith. The famous Rosetta Stone was carved from a slab of granodiorite, not basalt as famously believed for many years.
Field identification & locations
Identify by its coarse 'salt and pepper' appearance with more plagioclase feldspar than orthoclase. In the Ohio River Valley / Northern Kentucky region, finding such igneous rocks in nature usually indicates glacial transport from the Canadian Shield.
