igneous
Diorite
Diorite (an intermediate intrusive igneous rock)
Hardness: 6-7 on Mohs scale; Color: 'Salt and pepper' (mottled black/grey and white); Luster: Dull to sub-vitreous; Crystal structure: Phaneritic (coarse-grained); Specific gravity: 2.8-3.0.
- Hardness
- 6-7 on Mohs scale
- Color
- 'Salt and pepper' (mottled black/grey and white)
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6-7 on Mohs scale; Color: 'Salt and pepper' (mottled black/grey and white); 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 magma beneath the Earth's surface in volcanic arcs and mountain-building zones (subduction zones). It is typically of Proterozoic to Cenozoic age.
Uses & applications
Used primarily as a crushed stone for construction, road base, and drainage. High-quality specimens are polished for use as 'black granite' countertops, floor tiles, and gravestones.
Geological facts
The Code of Hammurabi was famously inscribed upon a seven-foot-tall stele of black diorite. It is often confused with gabbro or granite but is mineralogically intermediate between the two.
Field identification & locations
Identify in the field by its distinctive 'salt and pepper' appearance with crystals large enough to see with the naked eye. Commonly found in the Andes Mountains, Guernsey, and the Italian Alps.
