igneous
Diorite
Plutonic Igneous Rock (NaAlSi3O8, CaAl2Si2O8)
Hardness: 6-7 (Mohs scale), Color: Salt-and-pepper (mottled black and white), Luster: Phaneritic (crystalline minerals visible), Crystal Structure: Monoclinic/Triclinic minerals within a coarse-grained matrix, Cleavage: Good in two directions (feldspar grains), SG: 2.8-3.0
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Physical properties
Hardness: 6-7 (Mohs scale), Color: Salt-and-pepper (mottled black and white), Luster: Phaneritic (crystalline minerals visible), Crystal Structure: Monoclinic/Triclinic minerals within a coarse-grained matrix, Cleavage: Good in two directions (feldspar grains), SG: 2.8-3.0
Formation & geological history
Formed through the slow cooling of magma deep beneath the Earth's surface (intrusive). Commonly associated with subduction zones at volcanic arcs and convergent plate boundaries.
Uses & applications
Primarily used as a crushed 'base' material for roads and construction. In polished form, it is used for countertops, floor tiles, and as a dimension stone known commercially as 'black granite.'
Geological facts
The famous Code of Hammurabi, one of the oldest deciphered writings of length in the world, was inscribed on a 7-foot tall diorite stele.
Field identification & locations
Identify by its coarse 'salt-and-pepper' appearance. Unlike granite, it contains little to no visible quartz. Look for it in mountainous regions or volcanic arc roots; common in the Andes and Cascades.
