For mine, aluminium is wastefully extravagant (8)
I believe the answer is:
prodigal
'wastefully extravagant' is the definition.
(I've seen this before)
'for mine aluminium' is the wordplay.
'for' becomes 'pro' (I've seen this before).
'mine' becomes 'dig' (I've seen this before).
'aluminium' becomes 'al' (Al is the chemical symbol for aluminium).
'pro'+'dig'+'al'='PRODIGAL'
'is' is the link.
(Other definitions for prodigal that I've seen before include "Extravagant like Biblical son" , "Grip load (anag.)" , "This son got the fatted calf" , "Profligate" , "Extravagant - lavish" .)