Volcanic rock (4)
'volcanic rock' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for lava that I've seen before include "Volcanic stream" , "Molten volcanic material" , "Stuff heatedly hurled out" , "Volcanic emanation" , "Volcanic flowing rock" .)
'volcanic rock' is the definition.
(basalt is a kind of volcanic rock)
This is all the clue.
(Other definitions for basalt that I've seen before include "Rock containing olivine" , "Black volcanic rock" , "Common volcanic rock" , "rock from 2 [VOLCANO]" , "Dark rock of volcanic origin" .)