Granodiorite

Physical Properties

Hardness: 6-7 on Mohs scale; Color: Salt and pepper (grayish-white with dark flecks); Luster: Vitreous to dull; Crystal structure: Phaneritic (medium to coarse-grained), typically containing plagioclase feldspar, quartz, and hornblende or biotite.

Formation & Geological History

Formed through the slow cooling of magma deep beneath the Earth's surface (intrusive igneous rock). It is a major constituent of the Earth's continental crust and is commonly associated with mountain-building subduction zones.

Uses & Applications

Used primarily in construction as crushed stone for road bases, concrete, and railroad ballast. When polished, it is used for architectural facades, countertops, and monuments similar to granite.

Geological Facts

The famous Rosetta Stone was originally identified as basalt but was later correctly identified as being carved from a granodiorite slab.

Field Identification & Locations

Identify in the field by its interlocking crystalline texture and a higher proportion of plagioclase feldspar compared to potassium feldspar (making it gray rather than pink); commonly found in batholiths and large mountain ranges like the Sierra Nevada.

Identified on: 4/26/2026

Mode: Standard