Diorite

Physical Properties

Hardness: 6-7 on Mohs scale. Color: Salt and pepper (mottled black and white). Luster: Dull to sub-vitreous. Crystal Structure: Phaneritic (coarse-grained). Cleavage: Good (in feldspar and amphibole minerals). Specific Gravity: 2.8-3.0.

Formation & Geological History

Formed through the slow cooling of intermediate magma beneath the Earth's surface in volcanic arcs and mountain-building regions (subduction zones). It is found in large mountain ranges such as the Andes.

Uses & Applications

Used primarily as a crushed stone for road construction, drainage, and erosion control. Occasionally polished as ornamental stone or used as a durable dimension stone for monuments and floor tiles.

Geological Facts

Diorite is often called 'salt and pepper rock' due to its distinct black-and-white speckled appearance. In Ancient Egypt, it was highly prized for its extreme hardness and used to carve statues.

Field Identification & Locations

Identify by its coarse-grained texture and balanced mix of light (Plagioclase feldspar) and dark (Hornblende/Biotite) minerals. Unlike granite, it lacks significant visible quartz and potassium feldspar.

Identified on: 4/19/2026

Mode: Standard