Northern race excited by mother-of-pearl (5)
I believe the answer is:
nacre
'mother-of-pearl' is the definition.
('nacre' can be a synonym of 'mother-of-pearl')
'northern race excited by' is the wordplay.
'northern' becomes 'n' (abbreviation e.g. N. Ireland).
'excited' indicates an anagram.
'by' says to put letters next to each other.
'race' is an anagram of 'acre'.
'n'+'acre'='NACRE'
(Other definitions for nacre that I've seen before include "Pearl's mum" , "inside of shell" , "Constituent of inlay furniture" , "Mother of pearl" , "valuable material" .)