Granite Cobble

Physical Properties

Hardness: 6-7 (Mohs scale); Color: Pink to reddish-brown due to potassium feldspar; Luster: Dull (weathered) to vitreous (fresh surfaces); Structure: Phaneritic (coarse-grained visible crystals); Specific gravity: 2.63 - 2.75

Formation & Geological History

Formed from the slow cooling of magma deep beneath the Earth's surface (plutonic). This specific specimen has been rounded by mechanical weathering, likely in water (river or glacial action), which gives it its smooth, cobble-like shape.

Uses & Applications

Used in crushed form for road construction, as architectural stone (countertops, monuments), and larger rounded cobbles are popular in landscaping and decorative masonry.

Geological Facts

Granite is the most common rock found in the Earth's continental crust. Most granite dates from the Precambrian or Paleozoic eras. Pinker shades are typically caused by an abundance of Orthoclase feldspar.

Field Identification & Locations

Identify in the field by its salt-and-pepper or multi-colored crystalline appearance and its extreme hardness; it cannot be scratched by a steel knife. Common in volcanic ranges or areas with exposed glacial deposits.

Identified on: 4/29/2026

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