Mineral forms are a blast (9)
I believe the answer is:
alabaster
'mineral' is the definition.
(alabaster is a kind of mineral)
'forms are a blast' is the wordplay.
'forms' indicates anagramming the letters.
'are a' becomes 'area' (maths abbreviation).
'area'+'blast'='areablast'
'areablast' with letters rearranged gives 'ALABASTER'.
(Other definitions for alabaster that I've seen before include "Type of gypsum" , "Material for sculpting" , "Blast area for white mineral" , "White ornamental stone" , "White gypsum used for carving" .)