Granodiorite

Physical Properties

Hardness: 6-7 on Mohs scale. Color: Phaneritic texture with a salt-and-pepper appearance (gray/white/mottled). Luster: Dull to vitreous. Crystal structure: Medium to coarse-grained granular. Cleavage: Typically lacks cleavage as a whole, though mineral components like feldspar show it.

Formation & Geological History

Formed from the slow cooling and crystallization of silica-rich magma beneath the Earth's surface (plutonic). It is intermediate in composition between granite and diorite. Found in batholiths and large mountain-building regions.

Uses & Applications

Used primarily in heavy construction as crushed stone or road base. In aesthetic applications, it is used for countertops, floor tiles, and ornamental building stone (often sold commercially as 'granite').

Geological Facts

Granodiorite is the rock that makes up the famous Rosetta Stone, which was used to decipher Egyptian hieroglyphs. It is one of the most abundant intrusive rocks on the planet.

Field Identification & Locations

Identify in the field by its speckled appearance; it contains more plagioclase feldspar than orthoclase (potassium) feldspar, making it look 'grayer' than pinkish granites. Widely found in subduction zone mountain ranges like the Sierra Nevada or the Andes.

Identified on: 4/14/2026

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