igneous
Diorite (River Pebble)
Phaneritic Intermediate Plutonic Rock (Diorite)
Hardness: 6-7 on Mohs scale. Color: Salt-and-pepper (black and white) appearance. Luster: Dull to sub-vitreous. Crystal Structure: Phaneritic (coarse-grained). Cleavage: Distinct in feldspar grains. Specific Gravity: 2.8-3.0.
- Hardness
- 6-7 on Mohs scale
- Color
- Salt-and-pepper (black and white) appearance
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Salt-and-pepper (black and white) appearance. Luster: Dull to sub-vitreous. Crystal Structure: Phaneritic (coarse-grained). Cleavage: Distinct in feldspar grains. Specific Gravity: 2.8-3.0.
Formation & geological history
Formed through the slow cooling of silicate magma below the Earth's surface (intrusive), typically at subduction zones. This specimen has been rounded and polished by fluvial (river) erosion.
Uses & applications
Used primarily as crushed stone for road construction and drainage. High-quality varieties are used as ornamental building stone ('black granite') or for floor tiles and graveyard markers.
Geological facts
Diorite was used in ancient Egypt for making hard stone sculptures, such as the famous statue of Khafre. The Code of Hammurabi was inscribed on an 8-foot tall diorite stele.
Field identification & locations
Identify in the field by the 'salt and pepper' look where the white (plagioclase feldspar) and black (biotite/amphibole) minerals are roughly equal. Found commonly in mountainous regions or riverbeds downstream from batholiths.
