volcanic bomb

The volcanic bomb is a specimen of igneous rock uniquely formed by flight. Molten stone—a pyroclast—flung from a volcanic vent during eruption may adopt in flight a spherical, disc, teardrop, radial, spindle, or other shape as it cools, falling toward Earth. Like yeasty dough, the lump may form a crusted exterior before the bubbly interior hardens, hence the alternate term breadcrust bomb. A network of cracks on the surface may indicate the continued expansion of the interior after the crust began to harden.

Kim Stafford