igneous
Diorite
Phaneritic plutonic rock (dominated by plagioclase feldspar and hornblende)
Hardness: 6-7 on Mohs scale; Color: 'Salt and pepper' (black and white/gray); Luster: Dull to vitreous; Structure: Phaneritic (coarse-grained); Cleavage: Good in two directions (feldspar); Specific gravity: 2.8-3.0.
- Hardness
- 6-7 on Mohs scale
- Color
- 'Salt and pepper' (black and white/gray)
- Luster
- Dull to vitreous
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Physical properties
Hardness: 6-7 on Mohs scale; Color: 'Salt and pepper' (black and white/gray); Luster: Dull to vitreous; Structure: Phaneritic (coarse-grained); Cleavage: Good in two directions (feldspar); 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 typically dates from the Proterozoic to the Cenozoic eras.
Uses & applications
Used primarily as structural stone, crushed stone for road base, and decorative architectural stone (granite-like countertops or floor tiles). Historically used by ancient Egyptians and Mayans for sculpture.
Geological facts
Diorite was used to carve the famous Code of Hammurabi, one of the oldest deciphered writings of significant length in the world, due to its extreme durability and toughness.
Field identification & locations
Identify by its coarse-grained texture where dark minerals (hornblende/biotite) and light minerals (plagioclase) are roughly equal in abundance. Found in mountainous roots like the Andes or the Alps. For collectors: look for 'orbicular' varieties which are highly prized.
