igneous
Diorite
Diorite
Hardness: 6-7 on Mohs scale. Color: Black and white (salt and pepper appearance). Luster: Dull to sub-vitreous. Crystal Structure: Phaneritic (coarse-grained). Cleavage: Varies by mineral component (plagioclase and amphibole). Specific gravity: 2.8-3.0.
- Hardness
- 6-7 on Mohs scale
- Color
- Black and white (salt and pepper appearance)
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Black and white (salt and pepper appearance). Luster: Dull to sub-vitreous. Crystal Structure: Phaneritic (coarse-grained). Cleavage: Varies by mineral component (plagioclase and amphibole). 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 mountain-building regions. It is an intrusive igneous rock intermediate in composition between granite and gabbro.
Uses & applications
Used primarily as crushed stone for road construction and drainage. High-quality specimens are polished and used as 'black granite' for countertops, floor tiles, and cemetery monuments.
Geological facts
In ancient times, such as in Egypt and Mesopotamia, diorite was highly valued for sculpture because of its extreme hardness; the Code of Hammurabi was inscribed on a diorite stele.
Field identification & locations
Identify by its distinct 'salt and pepper' speckled appearance with roughly equal parts light and dark minerals. Found in continental crust, often in the roots of mountains. Collectors look for large, well-defined crystal grains.
