igneous
Diorite river pebble
Diorite (intermediate plutonic rock)
Hardness: 6-7 Mohs; Color: Mottled black and white ('salt and pepper'); Luster: Dull to phaneritic (crystalline); Crystal structure: Phaneritic (medium to coarse-grained); Texture: Salt-and-pepper appearance due to plagioclase feldspar and hornblende.
- Hardness
- 6-7 Mohs
- Color
- Mottled black and white ('salt and pepper')
- Luster
- Dull to phaneritic (crystalline)
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Physical properties
Hardness: 6-7 Mohs; Color: Mottled black and white ('salt and pepper'); Luster: Dull to phaneritic (crystalline); Crystal structure: Phaneritic (medium to coarse-grained); Texture: Salt-and-pepper appearance due to plagioclase feldspar and hornblende.
Formation & geological history
Formed by the slow cooling of magma deep beneath the Earth's surface (intrusive), often occurring near volcanic arcs or subduction zones. This specimen has been rounded into a pebble by fluvial or coastal erosion.
Uses & applications
Used in construction as crushed stone, road base, and architectural building stone. Polished slabs are used for countertops and floor tiles. Historically used for ancient carvings and inscriptions.
Geological facts
Diorite is often used in ancient sculpture because of its extreme hardness; the Code of Hammurabi was inscribed on a tall black diorite stele. It is often confused with granite but lacks significant quartz content.
Field identification & locations
Identify by the speckled 'salt and pepper' look where the black and white minerals are roughly equal in size. Commonly found as smooth pebbles in riverbeds or near mountain ranges where the Earth's crust has been uplifted and eroded.
