Diorite

Physical Properties

Hardness: 6-7 (Mohs); Color: Mottled black and white ('salt and pepper'); Luster: Phaneritic (crystalline), dull to sub-glassy; Structure: Coarse-grained; Cleavage: Good in two directions via feldspar and hornblende.

Formation & Geological History

Formed through the slow cooling of magma beneath the Earth's surface in volcanic arches or subduction zones. It has an intermediate chemical composition between granite and gabbro.

Uses & Applications

Used primarily in the construction industry as crushed stone for road bases and drainage. When polished, it is used as a dimension stone for floor tiles, granite-style countertops, and building facing.

Geological Facts

Diorite was an extremely popular stone for sculpture in ancient Egypt and Mesopotamia because it is very hard and durable; the famous Code of Hammurabi was inscribed on a diorite stele.

Field Identification & Locations

Identify by its 'salt and pepper' appearance with roughly equal amounts of dark minerals (hornblende/biotite) and light minerals (plagioclase feldspar). Look for interlocking crystals visible to the naked eye.

Identified on: 4/19/2026

Mode: Standard