igneous
Diorite (River Cobble)
Diorite (Intrusive Igneous Rock)
Hardness: 6-7 on Mohs scale. Color: Salt and pepper (mottled gray, white, and black). Luster: Dull to sub-vitreous. Crystal structure: Phaneritic (coarse-grained). Cleavage: Distinct in feldspar grains.
- Hardness
- 6-7 on Mohs scale
- Color
- Salt and pepper (mottled gray, white, and black)
- Luster
- Dull to sub-vitreous
Identified More igneous →
Explore Diorite (River Cobble) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6-7 on Mohs scale. Color: Salt and pepper (mottled gray, white, and black). Luster: Dull to sub-vitreous. Crystal structure: Phaneritic (coarse-grained). Cleavage: Distinct in feldspar grains.
Formation & geological history
Formed by the slow cooling of magma beneath the Earth's surface (plutonic). This specific specimen has been smoothed and rounded into a cobble by water erosion in a river or glacial environment.
Uses & applications
Used as a crushed stone for construction, road base, and occasionally as a decorative building stone or for countertops (often sold as 'black granite').
Geological facts
Diorite was frequently used in ancient Egypt and Mesopotamia for sculptures and stelae because of its extreme hardness; the famous Code of Hammurabi was inscribed on a diorite pillar.
Field identification & locations
Identify by its 'salt and pepper' appearance and lack of visible quartz compared to granite. Commonly found in volcanic arcs and mountain roots. Found globally in riverbeds near mountainous terrain.
