Scoria, Basaltic Pumice

Scoria - John Seach
(basaltic pummice)

Scoria is a rough cinder-like vesicular lava. It is the basaltic equivalent of pumice.
Expansion of gases produce the shape. Scoria is abundant on the slopes of Mt Etna (Sicily)
and Ambrym ash plain (Vanuatu) and many other volcanoes.