igneous
Diorite (River Pebble)
Intermediate Phaneritic Igneous Rock
Hardness: 6-7 on Mohs scale; 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 on Mohs scale
- Color
- Salt and pepper (mottled black and white)
- Luster
- Dull to sub-vitreous
Identified More igneous →
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 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 arcs and mountain-building zones. This specific specimen has been smoothed and rounded by water transport in a river or beach environment.
Uses & applications
Used as crushed stone for road construction, base material in landscaping, and occasionally as dimension stone for building facades or monuments. Small pebbles are often used in decorative garden features.
Geological facts
Diorite is often referred to as 'salt and pepper' rock due to its contrasting mineral colors. Historically, its extreme hardness made it a preferred material for stone carvings in ancient Egypt and Mesopotamia, including the Code of Hammurabi.
Field identification & locations
Identify by its coarse-grained texture and roughly equal balance of light-colored plagioclase feldspar and dark minerals like hornblende or biotite. It lacks the pinkish potassium feldspar found in granite and the metallic content of gabbro.
