igneous
Granodiorite
Granodiorite (containing Plagioclase, Quartz, and Biotite/Amphibole)
Hardness: 6-7 on Mohs scale. Color: Phaneritic (salt and pepper) texture with grey, white, and dark minerals. Luster: Dull to vitreous. Crystal structure: Massive, coarse-grained. Specific gravity: 2.6-2.7.
- Hardness
- 6-7 on Mohs scale
- Luster
- Dull to vitreous
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Phaneritic (salt and pepper) texture with grey, white, and dark minerals. Luster: Dull to vitreous. Crystal structure: Massive, coarse-grained. Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the slow cooling of silica-rich magma deep underground (plutonic). It is intermediate in composition between granite and diorite. Often associated with volcanic arc roots and batholiths.
Uses & applications
Commonly used as crushed stone for road construction, building foundations, and occasionally polished as ornamental stone or countertops labeled as 'granite' in the trade.
Geological facts
The Rosetta Stone was famously carved from a slab of granodiorite, not basalt as was originally thought. It is the most common intrusive rock in the Earth's crust by volume.
Field identification & locations
Identify by its 'salt and pepper' appearance and visible interlocking crystals. It has more plagioclase feldspar than orthoclase feldspar compared to true granite. Found in mountain ranges and volcanic island arcs.
