Igneous
Diorite
Intermediate plutonic igneous rock
Hardness: 6-7 (Mohs scale); Color: Salt-and-pepper (speckled black and white/gray); Luster: Sub-vitreous to dull; Crystal structure: Phaneritic (coarse-grained coarse crystals visible to the naked eye); Cleavage: Distinct in feldspar minerals; Specific gravity: 2.8 - 3.0.
- Hardness
- 6-7 (Mohs scale)
- Color
- Salt-and-pepper (speckled black and white/gray)
- Luster
- Sub-vitreous to dull
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Salt-and-pepper (speckled black and white/gray); Luster: Sub-vitreous to dull; Crystal structure: Phaneritic (coarse-grained coarse crystals visible to the naked eye); Cleavage: Distinct in feldspar minerals; 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 above subduction zones. Typically formed during the Phanerozoic eon, often associated with continental margins.
Uses & applications
Used primarily as a decorative stone in architecture, as a base material in construction (crushed stone), for grave markers, and historically for sculptures and tools due to its extreme hardness.
Geological facts
Diorite was used by ancient civilizations like the Egyptians and Akkadians for monumental sculpture. The famous Code of Hammurabi was inscribed on a massive black diorite stele.
Field identification & locations
Identify in the field by its phaneritic texture and 'salt and pepper' appearance caused by roughly equal amounts of light plagioclase feldspar and dark minerals like hornblende or biotite. Commonly found in batholiths and mountain ranges like the Andes.
