igneous
Diorite
Phaneritic intermediate plutonic rock (Diorite)
Hardness: 6-7 (Mohs scale); Color: Salt and pepper (mottled grey, white, black); Luster: Dull to sub-vitreous; Crystal Structure: Phaneritic (coarse-grained); Specific Gravity: 2.8-3.0
- Hardness
- 6-7 (Mohs scale)
- Color
- Salt and pepper (mottled grey, white, black)
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Salt and pepper (mottled grey, white, black); Luster: Dull to sub-vitreous; Crystal Structure: Phaneritic (coarse-grained); Specific Gravity: 2.8-3.0
Formation & geological history
Formed by the slow cooling of intermediate magma underground in volcanic arcs and mountain building zones (subduction zones). It is usually of Phanerozoic age but can be found in older cratons.
Uses & applications
Used as crushed stone for road construction and as dimension stone for building facades, countertops, and floor tiles. Historically used for carvings and monumental sculpture.
Geological facts
The Code of Hammurabi was inscribed on a black diorite stele. It is often referred to as 'salt and pepper' rock due to its contrasting light and dark mineral grains.
Field identification & locations
Identify by the lack of visible quartz (unlike granite) and a roughly equal balance of light plagioclase feldspar and dark minerals like hornblende or biotite. Common in the Andes Mountains and Cascade Range.
