igneous
Diorite
Phaneritic intermediate plutonic rock
Hardness: 6-7 (Mohs); Color: Salt and pepper (black/dark green and white); Luster: Dull to sub-vitreous; Crystal structure: Phaneritic (medium to coarse-grained); Cleavage: Perfect in two directions for feldspar components.
- Hardness
- 6-7 (Mohs)
- Color
- Salt and pepper (black/dark green and white)
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6-7 (Mohs); Color: Salt and pepper (black/dark green and white); Luster: Dull to sub-vitreous; Crystal structure: Phaneritic (medium to coarse-grained); Cleavage: Perfect in two directions for feldspar components.
Formation & geological history
Formed by the slow cooling of magma below the Earth's surface in volcanic arcs and mountain-building zones (subduction zones). It consists primarily of plagioclase feldspar and hornblende or pyroxene.
Uses & applications
Used as a base material in construction, as crushed stone for roads, and occasionally as structural stone or polished 'black granite' for countertops and flooring.
Geological facts
Diorite was extremely popular in ancient Egypt and Mesopotamia for sculptures because of its hardness; the famous Code of Hammurabi was inscribed on a diorite stele.
Field identification & locations
Identify by its coarse-grained 'salt and pepper' appearance with a lacks of visible quartz compared to granite. Commonly found in batholiths and mountain roots in areas like the Andes or the Alps.
