Sea pink in most of the fissure (6)
I believe the answer is:
thrift
'sea pink' is the definition.
(I know that sea pink can be written as Thrift)
'most of the fissure' is the wordplay.
'most of' means to remove the last letter.
'fissure' becomes 'rift' (rift is a kind of fissure).
'the' with its last letter taken off is 'th'.
'th'+'rift'='THRIFT'
'in' acts as a link.
(Other definitions for thrift that I've seen before include "Practise this to save money" , "Plant - saving - economy" , "Carefulness with money" , "Good husbandry" , "Maritime growth" .)