Hard stone in gold before (7)
I believe the answer is:
austere
'hard' is the definition.
(I've seen this before)
'stone in gold before' is the wordplay.
'stone' becomes 'st'.
'in' indicates putting letters inside.
'gold' becomes 'au' (Au is the chemical symbol for gold).
'before' becomes 'ere' (usually literary).
'au'+'ere'='auere'
'st' placed inside 'auere' is 'AUSTERE'.
(Other definitions for austere that I've seen before include "Strict in appearance" , "Bleak" , "Severe in manner" , "Severe or strict in attitude" , "Severe, lacking comforts" .)