igneous
Granodiorite
Granodiorite
Hardness: 6-7 (Mohs scale); Color: Salt-and-pepper (mottled grey, white, and black); Luster: Phaneritic (crystalline); Crystal structure: Coarse-grained intrusive; Cleavage: Dependent on mineral grains; Specific gravity: 2.6-2.7
- Hardness
- 6-7 (Mohs scale)
- Color
- Salt-and-pepper (mottled grey, white, and black)
- Luster
- Phaneritic (crystalline)
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Salt-and-pepper (mottled grey, white, and black); Luster: Phaneritic (crystalline); Crystal structure: Coarse-grained intrusive; Cleavage: Dependent on mineral grains; Specific gravity: 2.6-2.7
Formation & geological history
Formed through the slow cooling of silica-rich magma beneath the Earth's surface (plutonic). They are common in volcanic arcs and mountain-building regions (orogeny), dating from various eras, frequently the Phanerozoic.
Uses & applications
Used primarily as crushed stone for road construction, railroad ballast, and as a decorative stone for countertops, curbs, and building veneers.
Geological facts
Granodiorite is the rock that makes up the famous Rosetta Stone. It is chemically intermediate between granite and diorite, containing more plagioclase feldspar than orthoclase.
Field identification & locations
Identify by its phaneritic texture with visible flecks of dark minerals like biotite or hornblende against a light background. Commonly found in large batholiths like the Sierra Nevada Range. It reacts very slightly to acid only if calcium-rich minerals are exposed.
