igneous
Diorite
Intermediate Phaneritic Igneous Rock (Diorite)
Hardness: 6-7 on Mohs scale; Color: 'Salt and pepper' mixture of white, gray, and black; Luster: Vitreous to dull; Crystal structure: Phaneritic (coarse-grained coarse crystalline); Cleavage: Perfect in two directions for feldspars; Specific gravity: 2.8-3.0.
- Hardness
- 6-7 on Mohs scale
- Color
- 'Salt and pepper' mixture of white, gray, and black
- Luster
- Vitreous to dull
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Physical properties
Hardness: 6-7 on Mohs scale; Color: 'Salt and pepper' mixture of white, gray, and black; Luster: Vitreous to dull; Crystal structure: Phaneritic (coarse-grained coarse crystalline); Cleavage: Perfect in two directions for feldspars; Specific gravity: 2.8-3.0.
Formation & geological history
Formed by the slow cooling of intermediate-composition magma deep beneath the Earth's surface in volcanic arcs and mountain-building zones (subduction zones). It typically dates back to various tectonic events throughout Earth's history.
Uses & applications
Used primarily as crushed stone for road construction and as a base material in engineering. High-quality specimens are polished for use as 'black granite' countertops, floor tiles, and cemetery markers.
Geological facts
Diorite was used in ancient Egypt and Mesopotamia for sculptures and tablets because of its extreme hardness; the famous Code of Hammurabi was inscribed on a diorite stele.
Field identification & locations
Identify in the field by its distinctive 'speckled' or 'dalmatian' appearance with roughly equal amounts of light (plagioclase) and dark (hornblende/biotite) minerals. Found in large mountain ranges like the Andes or Cascades.
