igneous
Granodiorite
Granodiorite (NaCa0.5(AlSi3O8)2(Fe,Mg)2)
Hardness: 6-7 Mohs; Color: Grayish-tan, salt-and-pepper, or weathered brown; Luster: Dull (weathered) to Vitreous (fresh surface); Crystal structure: Phaneritic (medium to coarse-grained); Cleavage: Prominent in feldspar grains; Specific gravity: 2.6-2.7.
- Hardness
- 6-7 Mohs
- Color
- Grayish-tan, salt-and-pepper, or weathered brown
- Luster
- Dull (weathered) to Vitreous (fresh surface)
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Physical properties
Hardness: 6-7 Mohs; Color: Grayish-tan, salt-and-pepper, or weathered brown; Luster: Dull (weathered) to Vitreous (fresh surface); Crystal structure: Phaneritic (medium to coarse-grained); Cleavage: Prominent in feldspar grains; Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the slow cooling and crystallization of silica-rich magma beneath the Earth's surface (intrusive). They are typically found in batholiths and continental crust, often associated with subduction zones.
Uses & applications
Commonly used in large-scale construction as crushed stone for road base, concrete aggregate, and railroad ballast. When polished, it can be used as ornamental stone or countertops, similar to granite.
Geological facts
Granodiorite is the intermediate rock between granite and diorite. One of the most famous archaeological artifacts in the world, the Rosetta Stone, is carved into a block of granodiorite.
Field identification & locations
Identify in the field by its visible interlocking crystals of white-to-gray plagioclase, glassy quartz, and dark biotite or hornblende. Weathered specimens like this often show a brownish oxidation on the outer surface.
