Value diamonds found in a swamp (6)
I believe the answer is:
admire
'value' is the definition.
(admire can mean to value or appreciate)
'diamonds found in a swamp' is the wordplay.
'diamonds' becomes 'd' (abbreviation for the card suit diamonds).
'found in' means one lot of letters goes inside another.
'swamp' becomes 'mire' (I've seen this in another clue).
'a'+'mire'='amire'
'd' placed within 'amire' is 'ADMIRE'.
(Other definitions for admire that I've seen before include "Have respect for, esteem" , "Regard with respect and approval" , "Look at (someone or something) with pleasure" , "Esteem. value" , "Esteem, have high regard for" .)