Granodiorite

Physical Properties

Hardness: 6-7 Mohs; Color: Salt and pepper (gray, white, black); Luster: Vitreous to dull; Crystal structure: Phaneritic (coarse-grained); Specific gravity: 2.6-2.8

Formation & Geological History

Formed from the slow cooling of magmas beneath the Earth's surface (intrusive). Commonly found in continental crust and volcanic arcs above subduction zones.

Uses & Applications

Used widely in construction as crushed stone for road base, building stone (granite slabs), and as a decorative stone in monuments.

Geological Facts

The Rosetta Stone was famously carved from granodiorite, not basalt as originally thought. It contains more plagioclase feldspar than orthoclase, distinguishing it from true granite.

Field Identification & Locations

Identify by looking for visible crystals of white plagioclase, gray quartz, and black biotite or hornblende. It is found in large mountain ranges such as the Sierra Nevada in the USA.

Identified on: 4/14/2026

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