igneous
Diorite
Phaneritic Intermediate Plutonic Rock (Diorite)
Hardness: 6-7 (Mohs scale); Color: 'Salt and pepper' (mottled black and white/grey); Luster: Dull to sub-vitreous; Crystal structure: Phaneritic (coarse-grained); Cleavage: Two directions (from feldspar/hornblende content); Specific Gravity: 2.8-3.0
- Hardness
- 6-7 (Mohs scale)
- Color
- 'Salt and pepper' (mottled black and white/grey)
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6-7 (Mohs scale); Color: 'Salt and pepper' (mottled black and white/grey); Luster: Dull to sub-vitreous; Crystal structure: Phaneritic (coarse-grained); Cleavage: Two directions (from feldspar/hornblende content); Specific Gravity: 2.8-3.0
Formation & geological history
Formed by the slow cooling of magma beneath the Earth's surface (intrusive) in volcanic arcs and above subduction zones. Typically Proterozoic to Cenozoic in age.
Uses & applications
Used in construction as crushed stone or 'black granite' for countertops, floor tiles, and building veneers; historically used for sculpture and monuments (e.g., Code of Hammurabi).
Geological facts
Famous historical artifacts like the Code of Hammurabi stele were carved into diorite due to its immense durability. It is often confused with gabbro or granite but contains less quartz than granite and more plagioclase than gabbro.
Field identification & locations
Identify by its distinct medium-to-coarse 'salt and pepper' texture. Common in mountain roots such as the Andes, Cascades, and the Alps. Look for visible interlocking crystals of white plagioclase and dark hornblende or biotite.
