Granodiorite

Physical Properties

Hardness: 6-7 Mohs; Color: Salt and pepper (white/light gray with black flecks); Luster: Vitreous to pearly; Crystal structure: Phaneritic (coarse-grained); Cleavage: Specific to individual minerals; Specific gravity: 2.6-2.7

Formation & Geological History

Formed through the slow cooling of silica-rich magma deep underground (plutonic). Found in large batholiths forming the cores of mountain ranges, often dating from the Precambrian to the Cenozoic eras.

Uses & Applications

Used primarily in heavy construction, road building, and as dimension stone for countertops, floor tiles, and monuments. High-quality specimens are popular for educational use.

Geological Facts

Granodiorite is the rock that makes up the famous Rosetta Stone. It is intermediate between granite and diorite in chemical composition.

Field Identification & Locations

Identify by its coarse-grained texture and 'salt and pepper' appearance. Look for more plagioclase feldspar than orthoclase. Commonly found in batholiths like the Sierra Nevada mountain range.

Identified on: 4/26/2026

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