Granodiorite

Hardness: 6-7 (Mohs scale), Color: Salt and pepper (mottled grey, black, and white), Luster: Vitreous to dull, Crystal Structure: Phaneritic (coarse-grained), Cleavage: Perfect in feldspars, none in quartz, Specific Gravity: 2.6-2.7

Formed through the slow cooling of magma deep underground (intrusive). It is typical of the subduction zone magmatism and the roots of volcanic arcs. Found in massive batholiths that can be hundreds of millions of years old.

Commonly used as crushed stone for road construction, building materials, paving stones, and sometimes polished as 'granite' for countertops and monuments.

Granodiorite is the rock that makes up the famous Rosetta Stone, which was essential for deciphering Egyptian hieroglyphs. It is intermediate in composition between granite and diorite.

Identify by its 'salt and pepper' appearance with more plagioclase feldspar than orthoclase. It is commonly found in the Sierra Nevada mountains of California and the Scottish Highlands. Look for visible crystals of quartz, feldspar, and dark minerals like biotite or hornblende.