igneous
Diorite
Intermediate plutonic igneous rock
Hardness: 6-7 (Mohs); Color: Mottled black and white (salt and pepper); Luster: Sub-vitreous to dull; Crystal structure: Phaneritic (coarsegrained, visible crystals); Specific gravity: 2.8 - 3.0
- Hardness
- 6-7 (Mohs)
- Color
- Mottled black and white (salt and pepper)
- Luster
- Sub-vitreous to dull
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Physical properties
Hardness: 6-7 (Mohs); Color: Mottled black and white (salt and pepper); Luster: Sub-vitreous to dull; Crystal structure: Phaneritic (coarsegrained, visible crystals); Specific gravity: 2.8 - 3.0
Formation & geological history
Formed through the slow cooling of magma beneath the Earth's surface in volcanic arches or subduction zones. It represents an intermediate composition between granite and gabbro.
Uses & applications
Used primarily as crushed stone for road construction, drainage, and erosion control. Occasionally polished and used as decorative building stone, countertops, or cemetery markers.
Geological facts
The famous Code of Hammurabi was inscribed on a large diorite stele. In ancient Egypt and Mesopotamia, it was highly prized for its durability and ability to hold fine detail in carvings.
Field identification & locations
Identify by its 'salt and pepper' appearance caused by nearly equal amounts of light plagioclase feldspar and dark minerals like hornblende or biotite. Commonly found in mountainous regions such as the Andes or the Cascades.
