igneous
Diorite
Diorite (Intermediate intrusive igneous rock)
Hardness: 6-7 on Mohs scale. Color: Salt-and-pepper (mottled black and white). Luster: Dull to sub-vitreous. Structure: Phaneritic (coarse-grained). Cleavage: Variable based on mineral content (amphiboles and plagioclase). Specific gravity: 2.8-3.0.
- Hardness
- 6-7 on Mohs scale
- Color
- Salt-and-pepper (mottled black 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 and white). Luster: Dull to sub-vitreous. Structure: Phaneritic (coarse-grained). Cleavage: Variable based on mineral content (amphiboles and plagioclase). Specific gravity: 2.8-3.0.
Formation & geological history
Formed through the slow cooling of magma beneath the Earth's surface in volcanic arcs and at subduction zones. It represents an intermediate composition between granite and gabbro.
Uses & applications
Used primarily as crushed stone for road construction and drainage. High-quality varieties are used as dimension stone for buildings, countertops, and floor tiles. Historically used for sculpture and inscriptions (e.g., the Code of Hammurabi).
Geological facts
Diorite was one of the few stones chosen by ancient Egyptians and Mesopotamians for important statues due to its extreme hardness and durability. It is often referred to as 'black granite' in the commercial stone trade.
Field identification & locations
Identify in the field by its distinctive 'salt-and-pepper' look with roughly equal parts dark and light minerals and no visible quartz. Commonly found in large mountain ranges like the Andes or the Cascades.
