igneous
Diorite (Polished River Pebble)
Diorite (Intermediate intrusive igneous rock)
Hardness: 6-7 Mohs; Color: Salt-and-pepper (white plagioclase with black hornblende/biotite); Luster: Dull to sub-vitreous; Crystal Structure: Phaneritic (coarse-grained); Specific Gravity: 2.8-3.0
- Hardness
- 6-7 Mohs
- Luster
- Dull to sub-vitreous
Identified More igneous →
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Physical properties
Hardness: 6-7 Mohs; Color: Salt-and-pepper (white plagioclase with black hornblende/biotite); Luster: Dull to sub-vitreous; Crystal Structure: Phaneritic (coarse-grained); Specific Gravity: 2.8-3.0
Formation & geological history
Formed from the slow cooling of magma beneath the Earth's surface (intrusive) in volcanic arcs and mountain-building zones. This specific specimen has been rounded and smoothed by water erosion/alluvial processes.
Uses & applications
Used in construction as crushed stone, for floor tiles, countertop surfaces (often sold as 'black granite'), and as decorative landscaping stones.
Geological facts
Diorite was 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
Identified by its phaneritic texture with a balanced mix of light and dark minerals. Commonly found in roots of mountain ranges or as eroded pebbles in riverbeds and beaches.
