Diorite

Physical Properties

Hardness: 6-7 on Mohs scale. Color: Salt and pepper (mottled black and white). Luster: Phaneritic (coarse-grained), dull to vitreous. Crystal structure: Massive, phaneritic texture. Specific gravity: 2.8 - 3.0.

Formation & Geological History

Formed by the slow cooling of silicate magma below the Earth's surface (intrusive) in volcanic arcs and mountain building zones. It is commonly found in batholiths and sills within the continental crust.

Uses & Applications

Used primarily as a decorative stone, crushed stone for road construction base, and in the production of statues and memorials. It was used by ancient civilizations for sculpture due to its extreme hardness.

Geological Facts

In Ancient Egypt, diorite was so valued for its durability that it was used for the Code of Hammurabi stela and statues of kings like Gudea. It is often confused with granite but lacks significant visible quartz.

Field Identification & Locations

Identify in the field by its distinctive 'salt and pepper' appearance and the absence of visible quartz (unlike granite). It is mainly composed of plagioclase feldspar and hornblende. Common in the Andes and Western North America.

Identified on: 4/25/2026

Mode: Standard