Granodiorite

Physical Properties

Hardness: 6-7 (Mohs scale); Color: Salt and pepper (mottled white, gray, and black); Luster: Phaneritic (crystalline, dull to glassy on fresh faces); Crystal Structure: Granular/Coarse-grained; Cleavage: None (rock mass); Specific Gravity: 2.6–2.73

Formation & Geological History

Formed through the slow cooling of magma deep beneath the Earth's surface (intrusive plutonism). It is similar to granite but contains more plagioclase feldspar than orthoclase. It can range from Precambrian to Cenozoic in age.

Uses & Applications

Used widely in construction as crushed stone for road base, building stone (similar to 'Granite' in the trade), memorials, and paving.

Geological Facts

The famous Rosetta Stone, which was the key to deciphering Egyptian hieroglyphs, was carved from a slab of granodiorite (specifically, a dark variety). It is one of the most common rocks in the Earth's continental crust.

Field Identification & Locations

Identify by its 'salt and pepper' look with visible crystals of white plagioclase, gray quartz, and black hornblende or biotite. It is found in mountain ranges and batholiths worldwide, notably the Sierra Nevada in the USA.

Identified on: 4/27/2026

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