Gray Basalt Cobble

Hardness: 6 (Mohs scale), Color: Dark gray to black (weathered to lighter gray), Luster: Dull/Matte, Crystal structure: Aphanitic (fine-grained), Specific gravity: 2.8–3.0

Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the surface. This specific specimen has been rounded and smoothed by water transport in a river or coastal environment.

Used extensively in construction as aggregate, in road base, and for architectural stone. Smaller smooth cobbles are popular in landscaping and decorative masonry.

Basalt is the most common rock on the Earth's surface and actually makes up most of the ocean floor. It is also found on the Moon and Mars.

Identified by its fine-grained texture, heaviness for its size, and solid gray color. Look for it along riverbeds and volcanic coastlines. It lacks visible crystals to the naked eye.