Granodiorite with Biotite Mica

Physical Properties

Hardness: 6-7 (Mohs scale); Color: White, gray, and black speckled appearance; Luster: Vitreous to pearly; Crystal structure: Phaneritic (medium to coarse-grained); Cleavage: Perfect in one direction for the mica flakes.

Formation & Geological History

Formed through the slow cooling of silica-rich magma deep within the Earth's crust (plutonic formation), often associated with subduction zones and mountain-building events.

Uses & Applications

Used widely in the construction industry as crushed stone for roads, and as polished slabs for countertops, monuments, and architectural facings.

Geological Facts

Granodiorite is the intermediate rock between granite and diorite. The famous Rosetta Stone was carved into a slab of granodiorite.

Field Identification & Locations

Identify in the field by its 'salt and pepper' appearance and visible crystal grains. It is commonly found in large batholiths such as the Sierra Nevada in California.

Identified on: 4/23/2026

Mode: Standard