Mineral
Bomba volcánica
A volcanic bomb is a body ejected into the air which, on cooling, develops an internal cavity.
It is not defined by a specific mineral species but by its origin. Within it, vapours and element-rich fluids generate diverse secondary crystallisations. Its appeal lies there, as it is an infrequent and visually powerful phenomenon.
Etymology
From Italian "bomba", a volcanic projectile that solidifies in the air. Its interior may form a geode through uneven cooling and subsequent mineral infiltration.