igneous
Diorite
Intermediate Phaneritic Igneous Rock (Diorite)
Hardness: 6-7 Mohs; Color: Salt and pepper (mottled black and white); Luster: Dull to sub-vitreous; Crystal structure: Phaneritic (coarse-grained); Specific gravity: 2.8-3.0
- Hardness
- 6-7 Mohs
- Color
- Salt and pepper (mottled black and white)
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6-7 Mohs; Color: Salt and pepper (mottled black and white); Luster: Dull to sub-vitreous; Crystal structure: Phaneritic (coarse-grained); Specific gravity: 2.8-3.0
Formation & geological history
Formed by the slow cooling of magma deep underground, often in volcanic arcs above subduction zones or in mountain-building regions. Primarily composed of plagioclase feldspar and darker minerals like hornblende or biotite.
Uses & applications
Used in construction as crushed stone or road base; sometimes used as dimension stone for building facades, floor tiles, and countertops. Anciently used for carving sculptures due to its durability.
Geological facts
Diorite was used in ancient Egypt and Mesopotamia to create durable statues and monuments; the famous Code of Hammurabi was inscribed on a diorite stele.
Field identification & locations
Identify by the speckled 'salt and pepper' appearance with crystals of roughly equal size visible to the naked eye. Found in Orogenic belts and batholiths. Can be mistaken for granite but lacks significant quartz content.
