Granodiorite

Physical Properties

Hardness: 6-7 Mohs; Color: Salt and pepper (white/grey with dark spots); Luster: Vitreous to dull; Crystal structure: Phaneritic (coarse-grained); Cleavage: Perfect on feldspars; Specific gravity: 2.6-2.7.

Formation & Geological History

Formed through the slow cooling of silica-rich magma deep within the Earth's crust, typically in subduction zones above convergent plate boundaries. Most are associated with large batholiths of Mesozoic or Cenozoic age.

Uses & Applications

Extensively used in construction as crushed stone for road base, and as dimension stone for buildings, monuments, and countertops.

Geological Facts

The Rosetta Stone, the famous artifact that helped linguists decrypt Egyptian hieroglyphs, was carved into a block of granodiorite (initially thought to be basalt).

Field Identification & Locations

Field Identification: Look for a phaneritic texture with more plagioclase than orthoclase feldspar, often distinguished by 'salt and pepper' appearance. Common in the Sierra Nevada mountains of California.

Identified on: 5/3/2026

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