igneous
Diorite
Intermediate plutonic igneous rock
Hardness: 6-7 on Mohs scale. Color: Salt and pepper appearance, predominantly dark gray to black with white speckles. Luster: Vitreous to dull. Crystal structure: Phaneritic (coarse-grained, visible interlocking mineral crystals). Specific gravity: 2.7-3.0.
- Hardness
- 6-7 on Mohs scale
- Luster
- Vitreous to dull
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Salt and pepper appearance, predominantly dark gray to black with white speckles. Luster: Vitreous to dull. Crystal structure: Phaneritic (coarse-grained, visible interlocking mineral crystals). Specific gravity: 2.7-3.0.
Formation & geological history
Formed from the slow cooling of intermediate magma beneath the Earth's surface, typically in subduction zone environments above continental margins.
Uses & applications
Used in construction, as crushed stone for road bases, as a building stone, and historically as an architectural and sculptural material (such as by ancient Egyptian and Mesopotamian civilizations).
Geological facts
Diorite is extremely hard and tough, which made it a favorite for ancient peoples to carve statues and build monuments before the widespread use of hardened steel tools. The famous Code of Hammurabi stele is carved from diorite.
Field identification & locations
Identify in the field by its distinct 'salt and pepper' look, composed mainly of plagioclase feldspar and dark amphibole or biotite. Commonly found in mountain belts and areas of ancient volcanic arcs.
