igneous
Diorite
Diorite, a coarse-grained intrusive igneous rock composed chiefly of plagioclase feldspar and hornblende, commonly with biotite or pyroxene
AI-generated identification · may be incorrectSpeckled gray-and-black appearance with visible interlocking crystals; typically hardness 6–7 Mohs, nonmetallic luster, and no consistent cleavage as a whole rock. The image is consistent with diorite, though a photo alone cannot confirm its mineral proportions.
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Physical properties
Speckled gray-and-black appearance with visible interlocking crystals; typically hardness 6–7 Mohs, nonmetallic luster, and no consistent cleavage as a whole rock. The image is consistent with diorite, though a photo alone cannot confirm its mineral proportions.
Formation & geological history
Forms when intermediate-composition magma cools slowly underground, allowing crystals to grow; found in ancient and modern continental mountain belts, with specimens spanning many geological ages.
Uses & applications
Used as crushed aggregate, dimension stone, paving, and sometimes decorative stone; less commonly used for carvings or polished objects.
Geological facts
Diorite’s contrasting light plagioclase and dark amphibole give it a distinctive “salt-and-pepper” look; it is compositionally between granite and gabbro.
Field identification & locations
Look for coarse, interlocking light feldspar and dark minerals, with little or no quartz; common in intrusive bodies and cobbles derived from them. Confirming identification requires examining a fresh surface or thin section.
