Diorite

Physical Properties

Hardness: 6-7 (Mohs). Color: 'Salt and pepper' (mottled black and white). Luster: Vitreous to sub-vitreous. Crystal Structure: Phaneritic (coarse-grained). Specific Gravity: 2.8-3.0.

Formation & Geological History

Formed through the slow cooling of silicate magma below the Earth's surface (intrusive) in volcanic arcs and mountain building zones. It is typically found in batholiths and laccoliths from various geological eras.

Uses & Applications

Used in construction as crushed stone for road bases and infrastructure. High-quality slabs are polished for use as countertops, floor tiles, and building veneers. Historically used for sculpture and tools.

Geological Facts

The Code of Hammurabi was famously inscribed on a large black diorite stele. Diorite is often mistaken for granite, but contains little to no quartz.

Field Identification & Locations

Identify in the field by its distinctive black-and-white speckled appearance and medium-to-large interlocking crystals. It lacks the pinkish hue of potassium feldspar found in granites. Commonly found in subduction zones.

Identified on: 4/29/2026

Mode: Standard