Basalt Pebble

Hardness of 6 on the Mohs scale, dark gray to black color, dull to sub-vitreous luster, fine-grained microcrystalline or cryptocrystalline structure, specific gravity around 2.8-3.0.

Formed from the rapid cooling of low-viscosity basaltic lava exposed at or very near the surface of a planet or moon. Geological age varies widely depending on the specific flow, ranging from recent volcanic activity to billions of years old.

Used widely in construction (as crushed stone for road base, concrete aggregate, and railroad ballast), manufacturing of stone wool insulation, and occasionally as decorative landscaping stones.

Basalt is the most common rock type in the Earth's crust underlying the oceans and also makes up significant portions of the volcanic plains on the Moon and Mars.

Easily identified by its dark, fine-grained appearance, often water-worn into smooth pebbles in riverbeds or coastal environments. Common worldwide wherever volcanic activity has occurred.