Diorite

Physical Properties

Hardness: 6-7 (Mohs scale); Color: Salt and pepper (mottled black and white/gray); Luster: Phaneritic (crystalline, dull to sub-glassy); Crystal structure: Coarse-grained; Specific gravity: 2.8-3.0.

Formation & Geological History

Formed through the slow cooling of magma deep beneath the Earth's surface (intrusive). It is intermediate in composition between granite and gabbro, typically found above subduction zones at volcanic arcs.

Uses & Applications

Used in construction as a base material for roads and buildings, frequently crushed for gravel. Polished varieties are used as Dimension Stone for countertops, floor tiles, and grave markers.

Geological Facts

In antiquity, particularly in Ancient Egypt and Mesopotamia, diorite was highly valued for sculpture because of its extreme hardness; the Code of Hammurabi was inscribed on a diorite stele.

Field Identification & Locations

Identify in the field by its speckled 'salt and pepper' appearance and visible individual crystals of roughly equal size. Typically lacks the pinkish potassium feldspar found in granite.

Identified on: 4/16/2026

Mode: Standard