Basalt (River Pebble)

Hardness (6 Mohs), dark gray to black color, dull/earthy luster, fine-grained (aphanitic) texture, high density/specific gravity (~2.8-3.0), non-foliated

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 smoothed by water erosion in a river or coastal environment.

Crushed stone for road base, concrete aggregate, railroad ballast, and high-quality specimens are used for 'hot stone' massage therapy or aquarium decor.

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

Identified by its heavy weight, dark color, and lack of visible crystals to the naked eye. Commonly found in volcanic regions, riverbeds, and beaches near tectonic plate boundaries.