igneous
Diorite (Salt and Pepper Rock)
Diorite
Hardness: 6-7 on Mohs scale; Color: Mottled black and white (salt-and-pepper); Luster: Dull to phaneritic (visible crystals); Crystal structure: Coarse-grained phaneritic; Cleavage: Good in two directions (due to feldspar and amphibole); Specific gravity: 2.8-3.0.
- Hardness
- 6-7 on Mohs scale
- Color
- Mottled black and white (salt-and-pepper)
- Luster
- Dull to phaneritic (visible crystals)
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Mottled black and white (salt-and-pepper); Luster: Dull to phaneritic (visible crystals); Crystal structure: Coarse-grained phaneritic; Cleavage: Good in two directions (due to feldspar 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 zones (subduction zones). It is plutonic/intrusive in nature.
Uses & applications
Used primarily in construction as crushed stone for road base or building stone. High-quality specimens are polished for use as countertops, floor tiles, and grave markers.
Geological facts
Diorite was used by ancient civilizations for sculpture because of its extreme hardness and durability; the famous Code of Hammurabi slab is carved into a black diorite-like rock.
Field identification & locations
Identify by its coarse 'salt and pepper' look where the dark minerals (hornblende/biotite) and light minerals (plagioclase feldspar) are roughly equal in size. Commonly found in roots of mountain ranges.
