Material question: cracked up over that (6)
I believe the answer is:
damask
'material' is the definition.
(damask is a kind of material)
'question cracked up over that' is the wordplay.
'question' becomes 'ask'.
'cracked up' becomes 'dam' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'over that' means one lot of letters go next to another.
'ask' after 'dam' is 'DAMASK'.
Can you help me to learn more?
(Other definitions for damask that I've seen before include "Table linen material" , "Rich, heavy fabric with a pattern woven into it, a tablecloth say" , "Patterned table linen" , "Patterned cloth" , "Reversible fabric - type of rose" .)