Diorite (Salt and Pepper Rock)

Physical Properties

Hardness: 6-7 on Mohs scale. Color: Black and white (mottled). Luster: Sub-vitreous. Crystal Structure: Phaneritic (coarse-grained). Cleavage: Distinct in feldspar and hornblende grains. Specific Gravity: 2.8-3.0.

Formation & Geological History

Formed by the slow cooling of silicate magma below the Earth's surface in volcanic arcs and mountain-building regions. It is intermediate in composition between granite and gabbro.

Uses & Applications

Widely used in construction as crushed stone or 'road base.' High-quality polished specimens are used as architectural facing stone, countertops, and floor tiles. Historically used for carving sculptures.

Geological Facts

The Code of Hammurabi was famously inscribed on a 7-foot tall diorite stele. It is often mistaken for granite but lacks significant visible quartz grains.

Field Identification & Locations

Identify in the field by its characteristic 'salt and pepper' appearance with roughly equal parts dark and light minerals. Found in large batholiths or sills in mountainous regions like the Andes or Cascades.

Identified on: 4/26/2026

Mode: Standard