igneous
Diorite
Intermediate plutonic igneous rock
Hardness: 6-7 on Mohs scale; Color: Black and white (salt and pepper appearance); Luster: Phaneritic (coarse-grained) with vitreous minerals; Crystal Structure: Equigranular; Specific Gravity: 2.8-3.0
- Hardness
- 6-7 on Mohs scale
- Color
- Black and white (salt and pepper appearance)
- Luster
- Phaneritic (coarse-grained) with vitreous minerals
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Black and white (salt and pepper appearance); Luster: Phaneritic (coarse-grained) with vitreous minerals; Crystal Structure: Equigranular; Specific Gravity: 2.8-3.0
Formation & geological history
Formed through the slow cooling of silicate magma below the Earth's surface (intrusive) in volcanic arcs and mountain-building regions above subduction zones.
Uses & applications
Used primarily as crushed stone for construction, road base, and as a decorative building stone (often sold as 'black granite') for countertops, paving, and monuments.
Geological facts
The famous Code of Hammurabi was inscribed on a 7-foot tall stele made of black diorite. It is often referred to as 'salt and pepper' rock due to its contrasting mineral colors.
Field identification & locations
Identify in the field by its coarse grain size and roughly equal balance of light (plagioclase feldspar) and dark (hornblende or biotite) minerals. Commonly found in large batholiths along continental margins.
