igneous
Diorite
Diorite (plagioclase-rich phaneritic rock)
Hardness: 6-7 Mohs; Color: Salt and pepper (mottled black and white); Luster: Sub-vitreous to dull; Crystal structure: Phaneritic (coarse-grained); Specific gravity: 2.8-3.0
- Hardness
- 6-7 Mohs
- Color
- Salt and pepper (mottled black and white)
- Luster
- Sub-vitreous to dull
Identified More igneous →
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Physical properties
Hardness: 6-7 Mohs; Color: Salt and pepper (mottled black and white); Luster: Sub-vitreous to dull; Crystal structure: Phaneritic (coarse-grained); Specific gravity: 2.8-3.0
Formation & geological history
Formed from the slow cooling of magma beneath the Earth's surface in volcanic arcs and mountain-building zones (subduction zones). Compositionally intermediate between granite and gabbro.
Uses & applications
Used primarily as decorative stone, crushed stone for construction, and as base material for roads. High-quality specimens are polished for countertops or cemetery markers.
Geological facts
Diorite was used in ancient Egypt and Mesopotamia for sculptures and tablets because it is extremely hard and durable; the Code of Hammurabi was inscribed on a diorite stele.
Field identification & locations
Identify in the field by its distinctive 'chunky' interlocking crystals of white feldspar and dark hornblende/biotite. Found in continental crust regions with deep-seated igneous activity.
