Igneous
Diorite
Phaneritic Intermediate Plutonic Rock
Hardness: 6-7 on Mohs scale; Color: 'Salt and pepper' (black and white); Luster: Dull to sub-vitreous; Structure: Phaneritic (coarse-grained) crystalline; Specific Gravity: 2.8 - 3.0
- Hardness
- 6-7 on Mohs scale
- Color
- 'Salt and pepper' (black and white)
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6-7 on Mohs scale; Color: 'Salt and pepper' (black and white); Luster: Dull to sub-vitreous; Structure: Phaneritic (coarse-grained) crystalline; Specific Gravity: 2.8 - 3.0
Formation & geological history
Formed by the slow cooling of intermediate-composition magma deep beneath the Earth's surface in intrusive bodies like batholiths or laccoliths. Often found above subduction zones.
Uses & applications
Used primarily in construction as crushed stone or road base. Due to its hardness, it is also polished for use as dimension stone, flooring, and kitchen countertops (often sold as 'black granite').
Geological facts
Diorite was used by ancient civilizations for sculpture and inscriptions because of its extreme hardness; the famous Code of Hammurabi was carved into a black diorite stele.
Field identification & locations
Identify in the field by its distinctive equigranular 'salt and pepper' appearance, lacking the pink potassium feldspar of granite. Common in mountainous regions like the Andes. Collectors look for even grain distribution.
