Mother-of-pearl source (7)
I believe the answer is:
abalone
'mother-of-pearl source' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for abalone that I've seen before include "Mollusc with an oval shell lined with bluish mother-of-pearl" , "Source of mother-of-pearl" , "marine creature" , "Edible mollusc - on a bale (anag)" , "Sea food must be found" .)