igneous
Diorite
Diorite
Hardness: 6-7 (Mohs scale); Color: 'Salt and pepper' (mottled black and white); Luster: Phaneritic (crystalline and dull to vitreous); Crystal Structure: Coarse-grained phaneritic; Cleavage: Good in two directions (due to feldspar and hornblende); Specific Gravity: 2.8-3.0.
- Hardness
- 6-7 (Mohs scale)
- Color
- 'Salt and pepper' (mottled black and white)
- Luster
- Phaneritic (crystalline and dull to vitreous)
Identified More igneous →
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Physical properties
Hardness: 6-7 (Mohs scale); Color: 'Salt and pepper' (mottled black and white); Luster: Phaneritic (crystalline and dull to vitreous); Crystal Structure: Coarse-grained phaneritic; Cleavage: Good in two directions (due to feldspar and hornblende); Specific Gravity: 2.8-3.0.
Formation & geological history
Formed by the slow cooling of intermediate-composition magma deep beneath the Earth's surface (plutonic). It usually occurs in volcanic arcs and mountain-building regions above subduction zones.
Uses & applications
Used primarily as crushed stone for road construction and as a decorative building material ('black granite'). In ancient times, it was used for sculpture due to its extreme hardness.
Geological facts
The famous Code of Hammurabi was inscribed on a massive black diorite stele. It is often referred to as 'Black Granite' in the commercial stone trade, though geologically they are distinct.
Field identification & locations
Identify by its characteristic speckled appearance where dark minerals (biotite/hornblende) and light minerals (plagioclase) are present in roughly equal amounts. Commonly found in large batholiths in the Andes and the Western United States.
