igneous
Granodiorite
Granodiorite (containing quartz, plagioclase, and biotite/hornblende)
Hardness: 6-7 on Mohs scale; Color: speckled 'salt and pepper' (gray, white, and black); Luster: phaneritic (crystalline/dull to vitreous); Crystal structure: coarse-grained granular; Cleavage: none (fractures); Specific gravity: approx 2.6-2.7
- Hardness
- 6-7 on Mohs scale
- Color
- speckled 'salt and pepper' (gray, white, and black)
- Luster
- phaneritic (crystalline/dull to vitreous)
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Physical properties
Hardness: 6-7 on Mohs scale; Color: speckled 'salt and pepper' (gray, white, and black); Luster: phaneritic (crystalline/dull to vitreous); Crystal structure: coarse-grained granular; Cleavage: none (fractures); Specific gravity: approx 2.6-2.7
Formation & geological history
Formed from the slow cooling of silica-rich magma deep underground (plutonic). It is intermediate between granite and diorite and is a major component of the Earth's continental crust, often found in large batholiths.
Uses & applications
Used extensively in construction as crushed stone for road base, concrete, and railroad ballast. When polished, it is sold as 'granite' for countertops, ornamental stone, and monuments.
Geological facts
The Rosetta Stone was originally mistake for granite but was later identified as being carved from granodiorite. It is one of the most common rocks in the Sierra Nevada mountain range.
Field identification & locations
Identify in the field by its speckled appearance and coarse grains where you can see the individual minerals. Unlike granite, it contains more plagioclase feldspar than orthoclase. Look for dark flakes of biotite mica.
