Glass makes blubber last — weird! (7)
I believe the answer is:
crystal
'glass' is the definition.
(I know that glass can be written as crystal)
'blubber last weird' is the wordplay.
'blubber' becomes 'cry' (to blubber is to cry uncontrollably).
'weird' indicates anagramming the letters.
'last' is an anagram of 'stal'.
'cry'+'stal'='CRYSTAL'
'makes' acts as a link.
(Other definitions for crystal that I've seen before include "Transparent mineral" , "Glassware" , "Glass-like quartz" , "Cut-glass" , "Very clear glass" .)