igneous
Diorite
Diorite (Plagioclase feldspar and Hornblende/Biotite)
Hardness: 6-7 on Mohs scale; Color: 'Salt and pepper' appearance (dirty white to grey with green/black specks); Luster: Dull to sub-vitreous; Crystal structure: Phaneritic (coarse-grained); Specific gravity: 2.8-3.0.
- Hardness
- 6-7 on Mohs scale
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6-7 on Mohs scale; Color: 'Salt and pepper' appearance (dirty white to grey with green/black specks); Luster: Dull to sub-vitreous; Crystal structure: Phaneritic (coarse-grained); Specific gravity: 2.8-3.0.
Formation & geological history
Formed by the slow cooling of magma beneath the Earth's surface, typically above subduction zones at convergent plate boundaries. It is intermediate in composition between granite and gabbro.
Uses & applications
Used as a base material in road construction, as dimension stone for building facades, floor tiles, and historically for sculpture and tablets (e.g., the Code of Hammurabi).
Geological facts
Diorite was an extremely popular stone for sculpture in Ancient Egypt and Mesopotamia because it is very hard and durable, allowing it to hold a high polish and fine detail for millennia.
Field identification & locations
Identified by its medium-to-coarse interlocking salt-and-pepper grain pattern. Unlike granite, it lacks significant visible quartz. Commonly found in mountain roots (plutons) and volcanic arcs.
