Diorite

Physical Properties

Phaneritic (coarse-grained) texture; Mohs hardness of 6-7; salt-and-pepper appearance with black, white, and grey colors; dull to sub-vitreous luster; high specific gravity (~2.8-3.0).

Formation & Geological History

Formed through the slow crystallization of magma beneath the Earth's surface in intrusive environments, often associated with volcanic arcs and subduction zones.

Uses & Applications

Commonly used as a base material in road construction, as crushed stone for building, and occasionally as structural 'black granite' for countertops and floor tiles.

Geological Facts

Ancient civilizations, including the Egyptians and Maya, used diorite to carve statues and stelas because of its extreme hardness and durability. The famous Code of Hammurabi was carved on a diorite pillar.

Field Identification & Locations

Identify in the field by its coarse mineral grains of roughly equal amounts of light plagioclase feldspar and dark minerals like hornblende or biotite. It lacks the pink orthoclase found in granite and the higher density/darker hue of gabbro.

Identified on: 4/27/2026

Mode: Standard