igneous
Diorite
Intermediate plutonic igneous rock
Phaneritic (coarse-grained) texture with a distinctive 'salt and pepper' appearance created by roughly equal amounts of white/light plagioclase feldspar and dark amphibole (hornblende) or biotite mica. Hardness: 6-7 on Mohs scale. Luster: vitreous to pearly on cleavage planes.
- Hardness
- 6-7 on Mohs scale
- Luster
- vitreous to pearly on cleavage planes
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Physical properties
Phaneritic (coarse-grained) texture with a distinctive 'salt and pepper' appearance created by roughly equal amounts of white/light plagioclase feldspar and dark amphibole (hornblende) or biotite mica. Hardness: 6-7 on Mohs scale. Luster: vitreous to pearly on cleavage planes.
Formation & geological history
Formed through the slow cooling of intermediate magma deep beneath the Earth's surface in subduction zones and volcanic arcs above continental margins.
Uses & applications
Used as crushed stone for construction, aggregate in concrete, road base, and polished for architectural dimension stone, countertops, and grave markers.
Geological facts
Ancient civilizations like the Egyptians and Mesopotamians carved diorite into statues and stelae due to its extreme durability. The famous Code of Hammurabi is inscribed on a black diorite stele.
Field identification & locations
Identify in the field by its characteristic coarse-grained black-and-white speckled pattern, lack of abundant quartz compared to granite, and high plagioclase content. Commonly found in mountain-building belts worldwide.
