Diorite

Physical Properties

Hardness: 6-7 Mohs; Color: Salt-and-pepper (mottled black and white); Luster: Subvitreous to dull; Crystal structure: Phaneritic (coarse-grained); Specific gravity: 2.8 - 3.0

Formation & Geological History

Formed by the slow cooling of magma beneath the Earth's surface (intrusive). Usually occurs in volcanic arcs or as batholiths in cordilleran mountain ranges. Compositionally intermediate between granite and gabbro.

Uses & Applications

Used primarily as a construction material (crushed stone) for road bases and concrete. When polished, it is used for countertops, floor tiles, and as a dimension stone for architectural facings. Historically used in sculpting.

Geological Facts

One of the most famous historical uses of diorite was for the Code of Hammurabi, an ancient Babylonian law code inscribed on a large diorite stele over 7 feet tall.

Field Identification & Locations

Identify in the field by its distinctive 'salt-and-pepper' appearance. Unlike granite, it contains little to no visible quartz. It is found in large intrusive bodies like the Andes Mountains or along the Western coast of North America.

Identified on: 4/18/2026

Mode: Standard