igneous
Diorite
Diorite (Plagioclase-rich phaneritic intrusive)
Hardness: 6-7 (Mohs scale), Color: Salt-and-pepper (gray, black, white), Luster: Dull to sub-vitreous, Crystal Structure: Phaneritic (coarse-grained visible crystals), Specific Gravity: 2.8-3.0
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Physical properties
Hardness: 6-7 (Mohs scale), Color: Salt-and-pepper (gray, black, white), Luster: Dull to sub-vitreous, Crystal Structure: Phaneritic (coarse-grained visible crystals), Specific Gravity: 2.8-3.0
Formation & geological history
Formed by the slow cooling of magma beneath the Earth's surface in volcanic arcs and mountain building zones. It is typically associated with subduction zones.
Uses & applications
Used primarily as crushed stone for construction, road base, and drainage. High-quality specimens are polished for use as 'black granite' in countertops, flooring, and masonry.
Geological facts
Diorite was used by ancient civilizations, such as the Egyptians and Sumerians, to carve durable statues and steles. The Code of Hammurabi was famously inscribed on a diorite block.
Field identification & locations
Identify by its 'salt and pepper' appearance and lack of visible quartz compared to granite. It is commonly found in the roots of mountain ranges such as the Andes or Cascades.
