Diorite (River Pebble)

Physical Properties

Hardness: 6-7 (Mohs scale); Color: 'Salt and pepper' (black and white/grey); Luster: Phaneritic (crystalline) but dull when weathered; Crystal Structure: Medium to coarse-grained granular; Specific Gravity: 2.8-3.0.

Formation & Geological History

Formed through the slow cooling of magma beneath the Earth's surface in volcanic arcs and mountain-building zones. This specific specimen has been Rounded by fluvial (river) or glacial transport processes.

Uses & Applications

Used primarily as crushed stone for road construction and aggregate. High-quality slabs can be used as dimension stone for buildings and monuments (similar to granite).

Geological Facts

Diorite was used in ancient civilizations like Egypt and Mesopotamia for sculptures and tablets because it is extremely hard and durable; the Code of Hammurabi was inscribed on a diorite stele.

Field Identification & Locations

Identify by its interlocking 'salt and pepper' minerals (plagioclase feldspar and hornblende/biotite). Look for it in riverbeds near mountainous or volcanic regions. It lacks the pink orthoclase found in granite.

Identified on: 4/14/2026

Mode: Standard