Pressure on gold to turn into chunk (7)
I believe the answer is:
portion
'chunk' is the definition.
(thesaurus)
'pressure on gold to turn into' is the wordplay.
'pressure' becomes 'p' (abbreviation).
'on' is an insertion indicator (as in clothing 'on' a person).
'gold' becomes 'or' ('or' is the heraldic name for gold).
'to turn' is an anagram indicator (letters turn into something else).
'into' with letters rearranged gives 'tion'.
'or' going into 'tion' is 'ortion'.
'p'+'ortion'='PORTION'
(Other definitions for portion that I've seen before include "allotment" , "Piece of a whole" , "A lot of" , "Helping - fate" , "Serving" .)