Basalt Pebble

Hardness of 6 on the Mohs scale, typically gray to black in color, dull to sub-metamorphic luster, fine-grained (aphanitic) crystal structure, specific gravity around 2.8-3.0.

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

Used in construction, aggregate, road base, and landscaping.

Basalt is the most common rock type in the Earth's crust underlying the world's ocean basins and forms much of the volcanic islands such as Hawaii.

Can be identified in the field by its dark gray or black color, fine-grained texture (individual crystals are usually too small to see without a microscope), and frequent presence of tiny gas bubbles (vesicles). Found worldwide.