igneous
Diorite
Diorite, a coarse-grained intrusive igneous rock composed mainly of plagioclase feldspar and hornblende, with possible biotite or pyroxene
AI-generated identification · may be incorrectBlack-and-white, coarse crystalline, with a speckled “salt-and-pepper” appearance; typically Mohs 6–7, nonmetallic luster, and no preferred cleavage as a rock. The hand-sized specimen appears rough and naturally broken.
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Physical properties
Black-and-white, coarse crystalline, with a speckled “salt-and-pepper” appearance; typically Mohs 6–7, nonmetallic luster, and no preferred cleavage as a rock. The hand-sized specimen appears rough and naturally broken.
Formation & geological history
Forms when intermediate-composition magma cools slowly underground, allowing visible crystals to grow. Diorite occurs in ancient and modern plutonic bodies across many geologic ages.
Uses & applications
Used as dimension stone, paving and crushed aggregate; polished pieces can serve as decorative stone, and attractive hand specimens are collected.
Geological facts
Its contrasting light plagioclase and dark ferromagnesian minerals give it the classic salt-and-pepper look; it is compositionally intermediate between granite and gabbro.
Field identification & locations
Identify it by visible interlocking white feldspar and dark hornblende/biotite, rather than the abundant quartz typical of granite. It occurs in intrusive rock bodies worldwide, including mountain belts and continental arcs.
