Perhaps a rhinestone is a national symbol (8)

I believe the answer is:

shamrock

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'national symbol' is the definition.
(symbol of Ireland)

I cannot understand how the rest of the clue works.

(Other definitions for shamrock that I've seen before include "Irish national symbol" , "Native Irish trefoil" , "Clover-like plant" , "Clover leaf" , "Sign of first part of 10 [IRISH [SEA]]" .)

I've seen this clue in The Times.

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