igneous
Diorite
Diorite
Hardness: 6-7 on Mohs scale; Color: 'Salt and pepper' (mottled black and white); Luster: Sub-vitreous to dull; Crystal structure: Phaneritic (coarse-grained); Cleavage: Good (due to plagioclase/amphibole); Specific gravity: 2.8-3.0
- Hardness
- 6-7 on Mohs scale
- Color
- 'Salt and pepper' (mottled black and white)
- Luster
- Sub-vitreous to dull
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Physical properties
Hardness: 6-7 on Mohs scale; Color: 'Salt and pepper' (mottled black and white); Luster: Sub-vitreous to dull; Crystal structure: Phaneritic (coarse-grained); Cleavage: Good (due to plagioclase/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 consists of intermediate chemical composition between granite and gabbro.
Uses & applications
Used as a base material in construction of roads, buildings, and parking lots (crushed stone). High-quality specimens are polished for use as dimension stone, floor tiles, and grave markers. Ancient civilizations like Egypt used it for statues and sarcophagi due to its extreme hardness.
Geological facts
Diorite is the rock used to carve the famous Code of Hammurabi, one of the oldest deciphered writings of significant length in the world. Its salt-and-pepper look is caused by a mix of light-colored plagioclase feldspar and dark hornblende or pyroxene.
Field identification & locations
Identify in the field by its speckled coarse-grained texture and balanced mix of light and dark minerals. It lacks the pinkish potassium feldspar found in granite and lacks the high density and dark dominance of gabbro. Commonly found in roots of mountain ranges.
