igneous
Diorite (River Pebble)
Diorite
Hardness: 6-7 (Mohs scale); Color: Salt and pepper (mottled grey/white/black); Luster: Dull (weathered) to phaneritic (crystalline); Crystal structure: Coarse-grained intrusive; Cleavage: Good in feldspars; Specific gravity: 2.8-3.0
- Hardness
- 6-7 (Mohs scale)
- Color
- Salt and pepper (mottled grey/white/black)
- Luster
- Dull (weathered) to phaneritic (crystalline)
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Salt and pepper (mottled grey/white/black); Luster: Dull (weathered) to phaneritic (crystalline); Crystal structure: Coarse-grained intrusive; Cleavage: Good in feldspars; Specific gravity: 2.8-3.0
Formation & geological history
Formed by the slow cooling of magma beneath the Earth's surface (intrusive). This specific specimen is a water-worn river pebble, likely shaped by fluvial erosion over hundreds of years. Common in volcanic arches above subduction zones.
Uses & applications
Used in construction as crushed stone or 'trap rock', for building facades, floor tiles, and historically for statues and stele (e.g., Code of Hammurabi). Small pebbles like this are used in aquarium landscaping and decorative gardens.
Geological facts
Diorite was used in Ancient Egypt for intricate sculptures because of its extreme hardness. The Code of Hammurabi, one of the oldest deciphered writings of significant length in the world, is inscribed on a diorite stele.
Field identification & locations
Identified by its 'salt and pepper' look where light plagioclase feldspar mixes with dark minerals like hornblende or biotite. Frequently found in riverbeds or coastal areas near mountain ranges. Collectors should look for the characteristic coarse grain size without the high quartz content of granite.
