Basalt (River Stone)

Hardness: 6 (Mohs scale), Color: Dark grey to black, Luster: Dull/Submetallic, Crystal structure: Aphanitic (fine-grained), Cleavage: None, Specific gravity: 2.8–3.0

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

Commonly used in construction (crushed stone), decorative masonry, hot stone massage therapy, and as aquarium or garden landscaping.

Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. It is also common on the Moon and Mars.

Identify in the field by its dark color, heavy weight (density), and lack of visible crystals. Commonly found in volcanic regions, riverbeds, and beaches near tectonic plate boundaries.