igneous
Diorite
Intermediate Phaneritic Igneous Rock
Hardness: 6-7 on Mohs scale; Color: 'Salt and pepper' (black and white/gray); Luster: Sub-vitreous to dull; Crystal structure: Phaneritic (coarse-grained); Cleavage: Distinct in two directions for amphibole/feldspar components; Specific Gravity: 2.8-3.0.
- Hardness
- 6-7 on Mohs scale
- Color
- 'Salt and pepper' (black and white/gray)
- Luster
- Sub-vitreous to dull
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Physical properties
Hardness: 6-7 on Mohs scale; Color: 'Salt and pepper' (black and white/gray); Luster: Sub-vitreous to dull; Crystal structure: Phaneritic (coarse-grained); Cleavage: Distinct in two directions for amphibole/feldspar components; Specific Gravity: 2.8-3.0.
Formation & geological history
Formed from the slow cooling of magma beneath the Earth's surface in volcanic arcs or above subduction zones. It has an intermediate chemical composition between granite and gabbro and typically dates from various periods of tectonic activity throughout Earth's history.
Uses & applications
Used as a crushed stone for road construction, as a building stone for facades (often marketed as 'black granite'), and historically for tools and monumental sculptures due to its extreme hardness.
Geological facts
The Code of Hammurabi, one of the oldest deciphered writings of significant length in the world, was inscribed on a 7-foot tall diorite stele. It is harder than granite and was favored by ancient Egyptian and Mesopotamian sculptors.
Field identification & locations
Identify in the field by its speckled 'salt and pepper' appearance with roughly equal parts dark (hornblende/biotite) and light (plagioclase feldspar) minerals. Commonly found in large mountain ranges such as the Andes.
