igneous
Granodiorite
Granodiorite
Hardness: 6-7 on Mohs scale. Color: Light gray to salt-and-pepper. Luster: Dull to vitreous when crystals are fresh. Crystal Structure: Phaneritic (medium to coarse-grained). Composition: Quartz, Plagioclase feldspar, and minor Biotite/Hornblende.
- Hardness
- 6-7 on Mohs scale
- Color
- Light gray to salt-and-pepper
- Luster
- Dull to vitreous when crystals are fresh
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Light gray to salt-and-pepper. Luster: Dull to vitreous when crystals are fresh. Crystal Structure: Phaneritic (medium to coarse-grained). Composition: Quartz, Plagioclase feldspar, and minor Biotite/Hornblende.
Formation & geological history
Formed from the slow cooling of silica-rich magma deep within the Earth's crust (plutonic). It is a major component of batholiths and continental crust, often dating from the Precambrian to Cenozoic eras.
Uses & applications
Used extensively in construction as crushed stone for road base, concrete aggregate, and as 'granite' for countertops, curbing, and monumental masonry.
Geological facts
Granodiorite is the rock that makes up the famous Rosetta Stone. It is chemically intermediate between granite and diorite, containing more plagioclase than orthoclase feldspar.
Field identification & locations
Identify in the field by its visible interlocking crystals and characteristic light gray color with dark flecks. It is commonly found in mountain ranges like the Sierra Nevada. Look for a rock that is harder than steel and has a speckled 'salt and pepper' appearance.
