igneous
Diorite (River Cobble)
Intrusive Igneous Diorite
Hardness: 6-7 (Mohs scale); Color: Salt and pepper (mottled white/gray and black); Luster: Dull to phaneritic (visible crystals); Crystal Structure: Phaneritic (coarse-grained); Cleavage: Good in two directions (feldspar) and splintery (amphibole); Specific Gravity: 2.8-3.0.
- Hardness
- 6-7 (Mohs scale)
- Color
- Salt and pepper (mottled white/gray and black)
- Luster
- Dull to phaneritic (visible crystals)
Identified More igneous →
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Salt and pepper (mottled white/gray and black); Luster: Dull to phaneritic (visible crystals); Crystal Structure: Phaneritic (coarse-grained); Cleavage: Good in two directions (feldspar) and splintery (amphibole); Specific Gravity: 2.8-3.0.
Formation & geological history
Formed through the slow cooling of magma beneath the Earth's surface in volcanic arcs and mountain-building zones. This particular specimen is a water-worn cobble, indicating it was transported and rounded by river action over thousands of years.
Uses & applications
Commonly used as a base material in construction, road building (crushed stone), and occasionally as a decorative stone for countertops or drainage landscaping.
Geological facts
Diorite was used by Ancient Egyptians for statues and vases because of its extreme hardness. The Code of Hammurabi was famously inscribed on a black diorite stele over 7 feet tall.
Field identification & locations
Identify by its 'salt and pepper' appearance with roughly equal parts light (plagioclase feldspar) and dark (biotite/hornblende) minerals. Found in riverbeds or glacial deposits where granitic basement rocks are exposed in mountains.
