igneous
Diorite
Phaneritic Intermediate Igneous Rock
Hardness: 6-7 Mohs; Color: Salt and pepper (mottled black and white/grey); Luster: Sub-vitreous to dull; Crystal structure: Coarse-grained (phaneritic); Cleavage: Distinct in feldspar/amphibole components; Specific Gravity: 2.8-3.0.
- Hardness
- 6-7 Mohs
- Color
- Salt and pepper (mottled black and white/grey)
- Luster
- Sub-vitreous to dull
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Physical properties
Hardness: 6-7 Mohs; Color: Salt and pepper (mottled black and white/grey); Luster: Sub-vitreous to dull; Crystal structure: Coarse-grained (phaneritic); Cleavage: Distinct in feldspar/amphibole components; Specific Gravity: 2.8-3.0.
Formation & geological history
Formed by the slow cooling of magma beneath the Earth's surface in volcanic arcs and mountain building zones (subduction zones). Likely Proterozoic to Cenozoic in age depending on local geology.
Uses & applications
Used primarily as crushed stone for road construction, base material, and occasionally as dimension stone for building facades or monuments.
Geological facts
Diorite is often called 'Black Granite' in the commercial stone trade, but it contains little to no quartz compared to true granite. The famous Code of Hammurabi was inscribed on a large black diorite stele.
Field identification & locations
Identify by its coarse 'salt and pepper' appearance and lack of visible quartz. Commonly found in roots of mountain ranges (Andes, Cascades). Field ID through hardness and lack of reaction to HCl.
