igneous
Diorite
Diorite (Intermediate intrusive igneous rock)
Hardness: 6-7 on Mohs scale. Color: 'Salt and pepper' (mottled black and white). Luster: Phaneritic (crystalline, dull to sub-glassy). Crystal structure: Coarse-grained equigranular. Specific Gravity: 2.8-3.0.
- Hardness
- 6-7 on Mohs scale
- Color
- 'Salt and pepper' (mottled black and white)
- Luster
- Phaneritic (crystalline, dull to sub-glassy)
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Physical properties
Hardness: 6-7 on Mohs scale. Color: 'Salt and pepper' (mottled black and white). Luster: Phaneritic (crystalline, dull to sub-glassy). Crystal structure: Coarse-grained equigranular. Specific Gravity: 2.8-3.0.
Formation & geological history
Formed through the slow cooling of silicate magma below the Earth's surface in volcanic arcs and mountain-building zones (subduction zones). It is usually Mesozoic to Cenozoic in age but can be found in older cratons.
Uses & applications
Used primarily as crushed stone for road construction and aggregate. High-quality specimens are polished and used as 'black granite' for countertops, floor tiles, and ornamental building veneers.
Geological facts
Diorite was used in ancient Egypt and Mesopotamia for sculptures and tablets because of its extreme hardness; the famous Code of Hammurabi is inscribed on a diorite stele.
Field identification & locations
Identify by its coarse-grained texture and near-equal mix of dark (amphibole/biotite) and light (plagioclase feldspar) minerals. Found in large mountain ranges like the Andes or the Cascades.
