igneous
Diorite
Diorite (Intermediate intrusive igneous rock)
Hardness: 6-7 Mohs; Color: Salt-and-pepper (speckled black and white/grey); Luster: Dull to sub-vitreous; Crystal structure: Phaneritic (coarse-grained visible crystals); Cleavage: Distinct in feldspars; Specific gravity: 2.8-3.0.
- Hardness
- 6-7 Mohs
- Color
- Salt-and-pepper (speckled black and white/grey)
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6-7 Mohs; Color: Salt-and-pepper (speckled black and white/grey); Luster: Dull to sub-vitreous; Crystal structure: Phaneritic (coarse-grained visible crystals); Cleavage: Distinct in feldspars; Specific gravity: 2.8-3.0.
Formation & geological history
Formed by the slow cooling of intermediate-silica magma deep beneath the Earth's surface in subduction zones or volcanic arcs. It primarily dates from Various geological eras depending on tectonic local history.
Uses & applications
Used as a base material in construction, crushed stone for road building, and as a decorative building stone. Historically used for sculpture and monuments (e.g., Code of Hammurabi) due to its extreme durability.
Geological facts
Diorite is often called 'Black Granite' in the commercial stone trade, but geologically it contains little to no quartz compared to true granite. The Code of Hammurabi, one of the oldest deciphered writings in history, was carved into a diorite stele.
Field identification & locations
Identify in the field by its characteristic 'salt and pepper' appearance and visible interlocking crystals of white plagioclase feldspar and dark hornblende/biotite. Found in batholiths and mountain roots in areas like the Andes, the Cascades, and parts of the UK.
