igneous
Granodiorite (Gravel Pebble)
Granodiorite
Hardness: 6-7 on Mohs scale; Color: Salt and pepper (mottled grey, white, and black); Luster: Sub-vitreous to dull; Crystal structure: Phaneritic (coarse-grained); Cleavage: Distinct in feldspars.
- Hardness
- 6-7 on Mohs scale
- Color
- Salt and pepper (mottled grey, white, and black)
- Luster
- Sub-vitreous to dull
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Salt and pepper (mottled grey, white, and black); Luster: Sub-vitreous to dull; Crystal structure: Phaneritic (coarse-grained); Cleavage: Distinct in feldspars.
Formation & geological history
Formed from the slow cooling of silica-rich magma deep underground (plutonic). Typically associated with batholiths and volcanic arcs during the Phanerozoic eon.
Uses & applications
Commonly used as crushed stone/gravel in construction, road base, and landscaping. High-quality slabs are used for countertops and building facades under the trade name 'granite'.
Geological facts
Granodiorite is the most common rock in many continental margins and is chemically intermediate between granite and diorite. The famous Rosetta Stone was carved from a slab of granodiorite.
Field identification & locations
Identify by its coarse grain and 'salt and pepper' appearance. Look for visible quartz, plagioclase feldspar, and dark minerals like biotite or hornblende. Commonly found in mountain ranges and glacial deposits.
