igneous
Diorite
Diorite (Intermediate intrusive igneous rock)
Hardness: 6-7 (Mohs scale); Color: Black and white (salt and pepper appearance); Luster: Sub-vitreous to dull; Crystal structure: Phaneritic (coarse-grained); Cleavage: Two directions at nearly 90 degrees (plagioclase component); Specific gravity: 2.8-3.0
- Hardness
- 6-7 (Mohs scale)
- Color
- Black and white (salt and pepper appearance)
- Luster
- Sub-vitreous to dull
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Black and white (salt and pepper appearance); Luster: Sub-vitreous to dull; Crystal structure: Phaneritic (coarse-grained); Cleavage: Two directions at nearly 90 degrees (plagioclase component); Specific gravity: 2.8-3.0
Formation & geological history
Formed from the slow cooling of magma beneath the Earth's surface (plutonic) in volcanic arcs and mountain building zones. It contains mineral compositions intermediate between granite and gabbro.
Uses & applications
Used in construction as crushed stone or base material, dimension stone for building facades, tiling, and occasionally for carved sculptures in antiquity.
Geological facts
Diorite was used by the ancient Egyptians and Sumerians for making hard-wearing tools and statues, such as the famous Code of Hammurabi stele. It is often confused with granite but lacks significant quartz content.
Field identification & locations
Look for a coarse-grained texture with an equal mix of light (plagioclase feldspar) and dark (biotite, hornblende, or pyroxene) minerals. Common in larger igneous batholiths in coastal mountain ranges.
