Rock shattered by a blast (6)
I believe the answer is:
basalt
'rock' is the definition.
(basalt is a kind of rock)
'shattered by a blast' is the wordplay.
'shattered' indicates anagramming the letters.
'by' says to put letters next to each other.
'a'+'blast' is 'ablast'.
'ablast' is an anagram of 'BASALT'.
(Other definitions for basalt that I've seen before include "Rock containing olivine" , "Commonest type of solidified lava; dense, dark grey and fine-grained" , "rock from 2 [VOLCANO]" , "Type of rock is a blast, oddly" , "Black volcanic rock" .)