Diorite

Physical Properties

Hardness: 6-7 (Mohs); Color: Salt and pepper (mottled grey, white, black); Luster: Dull 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 Earth's surface, typically in volcanic arcs or above subduction zones. Can range from Precambrian to Cenozoic in age.

Uses & Applications

Primarily used as a crushed stone for construction, road base, and drainage. High-quality specimens are used as decorative stone, countertops, or for carving (e.g., Code of Hammurabi).

Geological Facts

The famous Code of Hammurabi stele was carved into a massive slab of black diorite. It is often called 'salt and pepper' rock due to its mixed light and dark mineral content.

Field Identification & Locations

Identify in the field by its phaneritic texture and a roughly equal mix of light and dark minerals. Common in continental crust and mountain ranges like the Andes.

Identified on: 4/23/2026

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