Granite Cobble

Physical Properties

Hardness: 6-7 on Mohs scale; Color: Mottled yellow-brown (likely from iron staining), cream, and black; Luster: Dull to vitreous; Crystal structure: Phaneritic (coarse-grained visible crystals of quartz, feldspar, and mica); Specific Gravity: 2.6-2.7

Formation & Geological History

Formed from the slow cooling of silica-rich magma deep underground. This specific specimen has been Rounded and polished by river or wave action, a process taking thousands of years.

Uses & Applications

Primarily used as decorative stone, construction aggregate, or landscaping rock. High-quality granites are used for countertops and monuments.

Geological Facts

Granite makes up a large part of the Earth's continental crust. Its strength and resistance to acid rain make it one of the most durable building materials known to humans.

Field Identification & Locations

Identify in the field by its 'salt and pepper' appearance and interlocking mineral grains. This rounded beach/river cobble is commonly found in glacial till or along coastlines where ancient mountains have eroded.

Identified on: 5/3/2026

Mode: Standard