igneous
Diorite
Phaneritic Intermediate Plutonic Rock
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 beneath the Earth's surface in volcanic arches and subduction zones. It represents an intermediate composition between granite and gabbro.
Uses & applications
Used primarily as crushed stone for road construction and drainage, and occasionally as dimension stone for architectural facades or cemetery markers. In ancient Egypt, it was used for carving statues.
Geological facts
The Code of Hammurabi was famously inscribed on a seven-foot-tall diorite stele. It is often called 'Black Granite' in the commercial stone industry, even though it is geologically distinct.
Field identification & locations
Identify by its characteristic speckled 'dalmatian' appearance. Common in areas with mountain-building activity like the Andes or Cascades. Look for equal parts light plagioclase feldspar and dark minerals like hornblende or biotite.
