igneous
Diorite (Salt and Pepper Rock)
Phaneritic plutonic igneous rock (sodium-rich plagioclase feldspar and hornblende)
Hardness: 6-7 on Mohs scale. Color: Black and white (salt and pepper appearance). Luster: Dull to sub-vitreous. Crystal Structure: Phaneritic (coarse-grained). 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). Specific Gravity: 2.8-3.0.
Formation & geological history
Formed by the slow cooling of magma beneath the Earth's surface (intrusive) in volcanic arcs and mountain-building zones above subduction zones. Can range from Precambrian to Cenozoic in age.
Uses & applications
Used primarily as a crushed stone for road construction and as a dimension stone for building facades, floor tiles, and countertop material. Historically used for carving sculptures and steles.
Geological facts
The Code of Hammurabi, one of the oldest deciphered writings of significant length in the world, was inscribed on a black diorite stele over seven feet tall.
Field identification & locations
Identify in the field by its coarse 'salt and pepper' texture with roughly equal amounts of light (plagioclase) and dark (hornblende/biotite) minerals. Found commonly in the roots of mountain ranges like the Andes or Cascades.
