igneous
Granodiorite
Granodiorite (phaneritic intrusive igneous rock)
Hardness: 6-7 on Mohs scale. Color: Salt-and-pepper appearance (mottled grey, white, and black). Luster: Dull to vitreous. Crystal structure: Phaneritic (coarse-grained). Cleavage: Varies by mineral constituent (feldspar has two directions). Specific gravity: 2.6-2.7.
- Hardness
- 6-7 on Mohs scale
- Color
- Salt-and-pepper appearance (mottled grey, white, and black)
- Luster
- Dull to vitreous
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Salt-and-pepper appearance (mottled grey, white, and black). Luster: Dull to vitreous. Crystal structure: Phaneritic (coarse-grained). Cleavage: Varies by mineral constituent (feldspar has two directions). Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the slow cooling of silica-rich magma beneath the Earth's surface in batholiths and mountain roots. Typically formed during orogenic (mountain-building) events across various geological ages from the Precambrian to the Cenozoic.
Uses & applications
Extensively used in construction as crushed stone for road base, concrete, and railroad ballast. Also used as dimension stone for building facades, paving, and occasionally counter tops (often sold commercially as 'granite').
Geological facts
Granodiorite is the intermediate between granite and diorite. The famous Rosetta Stone was carved from a slab of granodiorite, and many of the Great Pyramids' inner chambers utilize this durable rock.
Field identification & locations
Identify in the field by its coarse 'salt and pepper' texture; it contains significantly more plagioclase feldspar than orthoclase (potassium) feldspar compared to true granite. Common in subduction zones and large batholiths like the Sierra Nevada. High durability makes it a staple for stone collectors and builders.
