igneous
Diorite
Diorite (Intermediate intrusive igneous rock)
Hardness: 6-7 on Mohs scale; Color: 'Salt and pepper' mixture of black and white; Luster: Phaneritic (medium to coarse-grained) crystals; Composition: Plagioclase feldspar, biotite, and hornblende; Cleavage: Good in two directions (feldspar).
- Hardness
- 6-7 on Mohs scale
- Color
- 'Salt and pepper' mixture of black and white
- Luster
- Phaneritic (medium to coarse-grained) crystals
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Physical properties
Hardness: 6-7 on Mohs scale; Color: 'Salt and pepper' mixture of black and white; Luster: Phaneritic (medium to coarse-grained) crystals; Composition: Plagioclase feldspar, biotite, and hornblende; Cleavage: Good in two directions (feldspar).
Formation & geological history
Formed through the slow cooling of magma beneath the Earth's surface in volcanic arcs and mountain-building zones (subduction zones). It is chemically intermediate between granite and gabbro.
Uses & applications
Used primarily as a crushed stone for construction, road base, and drainage. In some cases, polished slabs are used for countertops, curbing, or building facings (often sold commercially as 'black granite').
Geological facts
Ancient Egyptians and Mayans used diorite to carve statues and inscriptions because of its extreme hardness and durability; the Code of Hammurabi was famously inscribed on a pillar of diorite.
Field identification & locations
Identify by its phaneritic (visible crystals) texture and distinct mottled black-and-white appearance with little to no visible quartz. Found in roots of mountain ranges such as the Andes or Cascades.
