igneous
Diorite with Xenolith
Intermediate Plutonic Igneous Rock (Diorite)
Hardness: 6-7 Mohs; Color: Salt and pepper (black/white/gray/red); Luster: Dull to sub-vitreous; Structure: Phaneritic (coarse-grained); Specific Gravity: 2.8-3.0
- Hardness
- 6-7 Mohs
- Color
- Salt and pepper (black/white/gray/red)
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6-7 Mohs; Color: Salt and pepper (black/white/gray/red); Luster: Dull to sub-vitreous; Structure: Phaneritic (coarse-grained); Specific Gravity: 2.8-3.0
Formation & geological history
Formed by the slow cooling of intermediate magma beneath the Earth's surface in volcanic arcs. The central inclusion is likely a xenolith—a piece of pre-existing rock captured by the magma.
Uses & applications
Used in construction as crushed stone for roads or as dimension stone for architectural facings, floor tiles, and grave markers. Sometimes sold as 'black granite'.
Geological facts
Diorite was used in ancient Egypt and Mesopotamia for sculptures and tablets because of its extreme hardness; the famous Code of Hammurabi was inscribed on a diorite stele.
Field identification & locations
Identify by its phaneritic 'salt and pepper' appearance with roughly equal parts light plagioclase feldspar and dark minerals like hornblende or biotite. Commonly found in subduction zone mountain belts like the Andes.
