Diorite

Physical Properties

Hardness: 6-7 Mohs; Color: Salt and pepper (black and white); Luster: Phaneritic (crystalline minerals visible); Crystal Structure: Granular/Coarse-grained; Specific Gravity: 2.8-3.0

Formation & Geological History

Formed from the slow cooling of magma beneath the Earth's surface (intrusive), typically in volcanic arcs and mountain building zones above subduction processes.

Uses & Applications

Used primarily as decorative stone, crushed stone for road construction base, and occasionally as 'black granite' for countertops or floor tiles.

Geological Facts

Diorite was used in ancient Egypt and Mesopotamia for sculptures and tablets because of its extreme hardness; the Code of Hammurabi was inscribed on a diorite stele.

Field Identification & Locations

Identify by its 'salt and pepper' appearance caused by roughly equal parts light plagioclase feldspar and dark hornblende/biotite. Found in continental crust mountain ranges like the Andes.

Identified on: 5/7/2026

Mode: Standard