igneous
Granodiorite
Granodiorite (Intermediate plutonic rock)
Hardness: 6-7 on Mohs scale. Color: Salt-and-pepper (gray, white, black, with occasional pinkish hues from orthoclase). Luster: Dull to phaneritic (crystalline). Crystal structure: Phaneritic (medium-to-coarse grained). Specific gravity: 2.6-2.7.
- Hardness
- 6-7 on Mohs scale
- Luster
- Dull to phaneritic (crystalline)
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Salt-and-pepper (gray, white, black, with occasional pinkish hues from orthoclase). Luster: Dull to phaneritic (crystalline). Crystal structure: Phaneritic (medium-to-coarse grained). Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the slow cooling of silica-rich magma beneath the Earth's surface (plutonic). Typically associated with magmatic arcs above subduction zones and continental crust formation. Most date from the Precambrian to Cenozoic eras.
Uses & applications
Used primarily as crushed stone for road construction, concrete aggregate, and railroad ballast. High-quality specimens are polished and used for countertops, floor tiles, and ornamental stonework (often sold as 'Granite' in the trade).
Geological facts
Granodiorite is the most common intrusive rock in the Earth's crust. The famous Rosetta Stone was carved from a slab of granodiorite, not basalt as was originally thought.
Field identification & locations
Identify in the field by its visible interlocking crystals and high plagioclase feldspar content relative to potassium feldspar. It is found in large batholiths like the Sierra Nevada in California. Collectors should look for fresh, unweathered surfaces to see the distinct crystal boundaries.
