Diorite

Physical Properties

Hardness: 6-7 (Mohs scale), Color: Salt-and-pepper (black and white/grey), Luster: Dull to sub-vitreous, Crystal Structure: Phaneritic (coarse-grained), Cleavage: Perfect in two directions for amphiboles; two at 90 degrees for feldspar, Specific Gravity: 2.8-3.0

Formation & Geological History

Formed by the slow cooling of magma beneath the Earth's surface in volcanic arcs and mountain-building regions. It is an intrusive rock typically found in large batholiths or sills.

Uses & Applications

Used primarily as a crushed stone for base material in roads and parking lots. Higher quality specimens are used for floor tiles, granite-like countertops, and cemetery monuments. In antiquity, it was prized for sculpture because of its extreme hardness.

Geological Facts

Diorite was notoriously difficult to carve in ancient times. The famous Code of Hammurabi, one of the earliest legal codes in history, was inscribed on a massive diorite stele over 7 feet tall.

Field Identification & Locations

Identify in the field by its 'salt and pepper' appearance and visible crystalline texture. It is darker than granite but lacks the quartz content. Commonly found in subduction zones like the Andes Mountains or the Cascades.

Identified on: 4/22/2026

Mode: Standard