Granodiorite

Physical Properties

Hardness: 6-7 on Mohs scale; Color: Salt and pepper (white to grey with black speckles); Luster: Phaneritic (crystalline); Crystal structure: Granular; Cleavage: None for the rock, though mineral components have individual cleavage.

Formation & Geological History

Formed through the slow cooling of silica-rich magma beneath the Earth's surface. It is an intrusive (plutonic) igneous rock often found in large batholiths associated with mountain building.

Uses & Applications

Used primarily in construction as crushed stone for road base, building foundations, and as 'granite' countertops and decorative architectural stone.

Geological Facts

Granodiorite is the rock that makes up the famous Rosetta Stone. It is intermediate in composition between granite and diorite, containing more plagioclase than orthoclase feldspar.

Field Identification & Locations

Identify in the field by its coarse-grained texture and the presence of visible quartz alongside dark mica or hornblende. It is commonly found in the roots of mountain ranges like the Sierra Nevada.

Identified on: 4/23/2026

Mode: Standard