Diorite

Physical Properties

Hardness: 6-7 (Mohs scale), Color: 'Salt and pepper' (mottled black and white), Luster: Phaneritic (visible crystals), Structure: Crystalline, Cleavage: Interlocking grains

Formation & Geological History

Formed through the slow cooling of magma beneath the Earth's surface in volcanic arcs and cordilleran mountain building zones.

Uses & Applications

Used primarily as crushed stone for road construction, as a building stone for facades (often marketed as 'black granite'), and in antiquity for carved sculptures/steles.

Geological Facts

The Code of Hammurabi, one of the oldest deciphered writings of significant length in the world, was inscribed on a 7-foot tall diorite stele.

Field Identification & Locations

Identify in the field by its characteristic speckled coarse-grained texture. It contains roughly equal parts light plagioclase feldspar and dark minerals like hornblende or biotite. It lacks the pinkish potassium feldspar found in granite.

Identified on: 4/29/2026

Mode: Standard