Diorite

Physical Properties

Hardness: 6-7 on Mohs scale; Color: 'Salt and pepper' (mottled black and white/grey); Luster: Sub-vitreous to dull; Crystal structure: Phaneritic (coarse-grained); Specific Gravity: 2.8-3.0.

Formation & Geological History

Formed by the slow cooling of intermediate-composition magma (between basaltic and granitic) deep within the Earth's crust, often in volcanic arcs and mountain-building zones (orogenic belts).

Uses & Applications

Used primarily as dimension stone for construction, road base (crushed stone), kitchen countertops, and occasionally for carved sculptures (e.g., the Code of Hammurabi stele).

Geological Facts

Diorite is often called 'Black Granite' in the commercial stone trade, though geologically it is distinct due to its lack of significant quartz. The famous Code of Hammurabi was inscribed on a large diorite pillar.

Field Identification & Locations

Identify by its phaneritic texture with a roughly equal mix of light plagioclase feldspar and dark minerals like hornblende or biotite. It is commonly found in the roots of mountain ranges like the Andes or the Alps.

Identified on: 4/24/2026

Mode: Standard