Crossword Genius

A rough heavy mass of solidified lava containing many cavities (6)

Ross

I believe the answer is:

scoria

(Other definitions for scoria that I've seen before include "Slag" , "Form of lava" , "Ejected frothy lava" .)

I've seen this clue in The Independent.
Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.