igneous
Diorite
Phaneritic Intermediate Igneous Rock
Hardness: 6-7 Mohs; Color: Salt-and-pepper (white and black/dark gray); Luster: Dull to sub-vitreous; Crystal Structure: Phaneritic (coarse-grained coarse crystals visible to the eye); Cleavage: Good in two directions (due to feldspar and amphibole); Specific Gravity: 2.8-3.0.
- Hardness
- 6-7 Mohs
- Color
- Salt-and-pepper (white and black/dark gray)
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6-7 Mohs; Color: Salt-and-pepper (white and black/dark gray); Luster: Dull to sub-vitreous; Crystal Structure: Phaneritic (coarse-grained coarse crystals visible to the eye); Cleavage: Good in two directions (due to feldspar and amphibole); Specific Gravity: 2.8-3.0.
Formation & geological history
Formed through the slow cooling of magma beneath the Earth's surface in volcanic arcs and mountain-building zones (subduction zones). It is typically of Precambrian to Cenozoic age.
Uses & applications
Used primarily as a crushed stone for construction base, road building, and drainage. High-quality specimens are used as 'black granite' for countertops, floor tiles, and ornamental stonework (sculptures).
Geological facts
In antiquity, diorite was highly prized for its extreme hardness. The Code of Hammurabi was inscribed on a massive stele of black diorite. It is often referred to as 'salt-and-pepper rock' because of its speckled appearance.
Field identification & locations
Identify by its coarse-grained texture and roughly equal balance of light and dark minerals. Common in batholiths and mountain ranges like the Andes. Collectors look for even distribution of minerals and lack of weathering.
