Irish emblem is not a genuine stone (8)
I believe the answer is:
shamrock
'irish emblem' is the definition.
(I've seen this in another clue)
'genuine stone' is the wordplay.
'genuine' becomes 'sham' (I can't explain this - if you can you should give a lot more credence to this answer).
'stone' becomes 'rock' (synonyms).
'sham'+'rock'='SHAMROCK'
'is not a' acts as a link.
This may not be correct. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for shamrock that I've seen before include "symbolic of Ireland" , "Pressed grape-juice" , "The national Irish trefoil" , "Irish national symbol" , "Clover leaf" .)