igneous
Granodiorite
Granodiorite (Na,Ca)(Al,Si)4O8
Hardness: 6-7 Mohs; Color: Salt and pepper (mottled grey, white, and pinkish-brown); Luster: Phaneritic (visible crystals), vitreous to dull; Crystal Structure: Massive, granular; Cleavage: Good in feldspar minerals.
- Hardness
- 6-7 Mohs
- Color
- Salt and pepper (mottled grey, white, and pinkish-brown)
- Luster
- Phaneritic (visible crystals), vitreous to dull
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Physical properties
Hardness: 6-7 Mohs; Color: Salt and pepper (mottled grey, white, and pinkish-brown); Luster: Phaneritic (visible crystals), vitreous to dull; Crystal Structure: Massive, granular; Cleavage: Good in feldspar minerals.
Formation & geological history
Formed through the slow cooling of silica-rich magma beneath the Earth's surface (intrusive/plutonic). They are commonly found in the roots of mountain belts (batholiths) and oceanic-continental subduction zones.
Uses & applications
Used primarily as crushed stone for road construction and as an ornamental architectural stone. High-quality slabs are sometimes sold as 'granite' for countertops.
Geological facts
Granodiorite is the intermediate step between granite and diorite. The famous Rosetta Stone was carved into a slab of granodiorite.
Field identification & locations
Identify in the field by its speckled appearance and 'salt and pepper' texture. It contains more plagioclase feldspar than orthoclase, often giving it a slightly darker look than true granite. Found ubiquitously in mountain ranges like the Sierra Nevada.
