igneous
Diorite (River Pebble)
Intermediate Phaneritic Igneous Rock (Diorite)
Hardness: 6-7 Mohs; Color: Salt-and-pepper (mottled grey, white, and black); Luster: Dull to sub-vitreous; Structure: Phaneritic (coarse-grained crystals); Composition: Plagioclase feldspar and Hornblende/Biotite.
- Hardness
- 6-7 Mohs
- Color
- Salt-and-pepper (mottled grey, white, and black)
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6-7 Mohs; Color: Salt-and-pepper (mottled grey, white, and black); Luster: Dull to sub-vitreous; Structure: Phaneritic (coarse-grained crystals); Composition: Plagioclase feldspar and Hornblende/Biotite.
Formation & geological history
Formed from the slow cooling of silicate magma below the Earth's surface (intrusive). The rounded shape indicates transport and erosion in a river or coastal environment, likely during the Holocene epoch.
Uses & applications
Used as crushed stone for road construction, building foundations, and occasionally as decorative landscaping stone or 'river rocks' for garden design.
Geological facts
Diorite was used in ancient Egypt and Mesopotamia for sculptures and stelas because of its extreme hardness; the famous Code of Hammurabi was inscribed on a large diorite slab.
Field identification & locations
Identified by its 'salt and pepper' appearance and lack of visible quartz compared to granite. Commonly found in riverbeds or glacial tills near mountain ranges.
