igneous
Diorite
Intrusive Igneous Diorite
Hardness: 6-7 on Mohs scale; Color: Salt-and-pepper (black and white); Luster: Dull to sub-vitreous; Texture: Phaneritic (coarse-grained); Composition: Mostly plagioclase feldspar and hornblende/biotite.
- Hardness
- 6-7 on Mohs scale
- Color
- Salt-and-pepper (black and white)
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Salt-and-pepper (black and white); Luster: Dull to sub-vitreous; Texture: Phaneritic (coarse-grained); Composition: Mostly plagioclase feldspar and hornblende/biotite.
Formation & geological history
Formed by the slow cooling of silicate magma below the Earth's surface (intrusive). Usually occurs in volcanic arcs and mountain building zones above subduction zones.
Uses & applications
Crushed stone for road construction, drainage, and concrete; occasionally polished for countertops, floor tiles, and building veneers ('black granite').
Geological facts
Diorite was used in ancient Egypt and Mesopotamia for sculptures because of its extreme hardness; the Code of Hammurabi was inscribed on a diorite stele.
Field identification & locations
Identify by its 'salt and pepper' look with equal speckled distribution of light and dark minerals. Common in larger decorative gravel beds and riverbeds in volcanic regions.
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Dark Igneous Rock (Likely Basalt or Diabase)
Basalt (extrusive igneous rock) or Diabase (intrusive igneous rock - also known as Dolerite), largely composed of plagioclase feldspar, pyroxene (augite), and sometimes olivine and amphibole. Exact mineralogy would require thin section analysis.
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