Basalt Pebble

Hardness of 6 on the Mohs scale, dark gray to black color, fine-grained (aphanitic) crystal structure, dull luster, high specific gravity around 2.9 to 3.0

Formed from the rapid cooling of low-viscosity, magnesium- and iron-rich lava exposed at or very near the Earth's surface, often shaped into a smooth pebble by wave action in water or rivers

Used in construction, aggregate for road building, railway ballast, and occasionally in landscaping or as a tumbling stone

Basalt is the most common rock type in the Earth's crust, making up most of the oceanic crust and forming massive geological features like the Columbia River Flood Basalts and the Giant's Causeway in Northern Ireland

Found worldwide in volcanic regions and along riverbeds or beaches where volcanic rocks have been weathered and rounded; identifiable by its dark color and fine-grained texture