igneous
Diorite
Diorite (Plagioclase-rich phaneritic rock)
Hardness: 6-7 Mohs; Color: Mottled black and white (salt and pepper); Luster: Subvitreous to dull; Texture: Phaneritic (coarse-grained); Cleavage: Two directions at 90 degrees for feldspar grains.
- Hardness
- 6-7 Mohs
- Color
- Mottled black and white (salt and pepper)
- Luster
- Subvitreous to dull
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Physical properties
Hardness: 6-7 Mohs; Color: Mottled black and white (salt and pepper); Luster: Subvitreous to dull; Texture: Phaneritic (coarse-grained); Cleavage: Two directions at 90 degrees for feldspar grains.
Formation & geological history
Formed through the slow cooling of magma beneath the Earth's surface (intrusive) in volcanic arcs and mountain building zones. It typically occurs in continental crust above subduction zones.
Uses & applications
Used primarily as crushed stone for construction, road base, and drainage. High-quality specimens are polished and used as 'black granite' for countertops, floor tiles, and cemetery monuments.
Geological facts
Diorite was used in ancient Egypt and Mesopotamia for sculptures and tablets because of its extreme hardness; the Code of Hammurabi was inscribed on a diorite stele.
Field identification & locations
Identify by its coarse-grained 'salt and pepper' appearance, lack of visible quartz (unlike granite), and high hardness. It is commonly found in the roots of mountain ranges like the Andes or the Alps.
