igneous
Diorite
Diorite (Intermediate intrusive igneous rock)
Hardness: 6-7 on Mohs scale. Color: Salt and pepper (mottled black and white). Luster: Phaneritic (medium to coarse-grained crystals). Crystal Structure: Plagioclase feldspar, biotite, and hornblende. Cleavage: Good in two directions (feldspar). Specific gravity: 2.8-3.0.
- Hardness
- 6-7 on Mohs scale
- Color
- Salt and pepper (mottled black and white)
- Luster
- Phaneritic (medium to coarse-grained crystals)
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Salt and pepper (mottled black and white). Luster: Phaneritic (medium to coarse-grained crystals). Crystal Structure: Plagioclase feldspar, biotite, and hornblende. Cleavage: Good in two directions (feldspar). Specific gravity: 2.8-3.0.
Formation & geological history
Formed by the slow cooling of magma beneath the Earth's surface in volcanic arcs and at subduction zones. It represents an intermediate composition between granite and gabbro.
Uses & applications
Commonly used as a base material in construction of roads, buildings, and parking areas. It is also used as dimension stone for countertops, floor tiles, and grave markers, often sold as 'black granite'.
Geological facts
Diorite was used by ancient civilizations like the Egyptians and Sumerians for monumental sculpture because of its extreme hardness; the Code of Hammurabi was famously inscribed on a pillar of diorite.
Field identification & locations
Identify in the field by its characteristic 'salt and pepper' appearance and lack of visible quartz (unlike granite). Can be found in large batholiths in mountain ranges like the Andes or the Cascades.
