igneous
Diorite
Intermediate Phaneritic Igneous Rock
Hardness: 6-7 Mohs; Color: Salt and pepper (mottled black and white); Luster: Sub-vitreous to dull; Crystal structure: Phaneritic (coarse-grained); Specific gravity: 2.8-3.0
- Hardness
- 6-7 Mohs
- Color
- Salt and pepper (mottled black and white)
- Luster
- Sub-vitreous to dull
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Physical properties
Hardness: 6-7 Mohs; Color: Salt and pepper (mottled black and white); Luster: Sub-vitreous to dull; 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 or at mountain-building subduction zones. Typically Mesozoic to Cenozoic in age depending on locality.
Uses & applications
Used as crushed stone for road construction and drainage. High-quality specimens are polished for use as countertops, floor tiles, and building veneers. Historically used for sculpture due to its hardness.
Geological facts
The Code of Hammurabi was famously inscribed on a black diorite stele. It is often confused with granite but lacks the significant quartz and potassium feldspar content that defines granite.
Field identification & locations
Identify by its phaneritic (coarse) texture and balanced mix of light (plagioclase) and dark (amphibole/biotite) minerals. Found in continental crust mountain belts like the Andes or Cascades.
