igneous
Diorite
Diorite (Intermediate intrusive igneous rock)
Phaneritic (coarse-grained) texture, salt-and-pepper appearance; Mohs hardness of 6-7; gray to dark gray color; dull to sub-glassy luster; primarily composed of plagioclase feldspar, hornblende, and biotite.
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Physical properties
Phaneritic (coarse-grained) texture, salt-and-pepper appearance; Mohs hardness of 6-7; gray to dark gray color; dull to sub-glassy luster; primarily composed of plagioclase feldspar, hornblende, and biotite.
Formation & geological history
Formed from the slow cooling of magma beneath the Earth's surface (intrusive) in volcanic arcs and mountain-building regions above subduction zones.
Uses & applications
Used extensively in construction as crushed stone for roads and drainage; used in architecture as dimension stone for countertops, floor tiles, and building veneers; historically used for sculpture (such as the Code of Hammurabi).
Geological facts
Diorite is often called black granite in the commercial stone trade, but it contains little to no quartz compared to true granite. The famous Code of Hammurabi was inscribed on a massive black diorite stele.
Field identification & locations
Identify in the field by its speckled white and black appearance with visible crystals of roughly equal size. It is common in batholiths and mountain ranges like the Andes or the Cascades.
