igneous
Diorite
Diorite (an intrusive igneous rock)
Hardness: 6-7 on Mohs scale; Color: 'Salt and pepper' (gray/white and black mix); Luster: Sub-vitreous to dull; Crystal structure: Phaneritic (coarse-grained); Specific gravity: 2.8-3.0.
- Hardness
- 6-7 on Mohs scale
- Color
- 'Salt and pepper' (gray/white and black mix)
- Luster
- Sub-vitreous to dull
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Physical properties
Hardness: 6-7 on Mohs scale; Color: 'Salt and pepper' (gray/white and black mix); Luster: Sub-vitreous to dull; Crystal structure: Phaneritic (coarse-grained); Specific gravity: 2.8-3.0.
Formation & geological history
Formed by the slow cooling of magma beneath the Earth's surface in volcanic arches and mountain building zones. It is an intermediate intrusive rock, meaning it sits between granite and gabbro in composition.
Uses & applications
Used primarily as crushed stone for road construction and drainage. It is also used as a decorative 'black granite' in counter tops and building facades when polished.
Geological facts
Diorite is extremely tough; the Ancient Egyptians used it for sculpting because it is harder than granite. The Code of Hammurabi, one of the oldest law codes in history, was carved into a diorite stele.
Field identification & locations
Identify in the field by its distinctive black-and-white speckled appearance and hard, interlocking minerals (plagioclase and hornblende/biotite). Commonly found in the roots of mountain ranges.
