Diorite

Physical Properties

Hardness: 6-7 on Mohs scale; Color: 'Salt and pepper' (mottled black and white); Luster: Phaneritic (crystalline/dull); Crystal structure: Coarse-grained phaneritic texture; Cleavage: Good in two directions (due to feldspar and amphibole).

Formation & Geological History

Formed by the slow cooling of magma beneath the Earth's surface in volcanic arcs or along subduction zones. It represents an intermediate composition between granite and gabbro.

Uses & Applications

Used primarily as a crushed stone for construction and base material; occasionally polished for ornamental stone, countertops, or grave markers. Historically used for carving by ancient civilizations.

Geological Facts

Ancient Egyptians used diorite to build tools and statues because of its extreme hardness. The Code of Hammurabi was famously inscribed on a pillar of diorite.

Field Identification & Locations

Identify in the field by its distinct speckling; unlike granite, it lacks or has very little visible quartz. It is commonly found in mountain roots (plutons) and at convergent plate boundaries.

Identified on: 4/24/2026

Mode: Standard