Ringo's exotic buy? A precious stone (4,4)

I believe the answer is:

star ruby

'a precious stone' is the definition.
(type of gemstone)

'ringo's exotic buy?' is the wordplay.
'ringo' becomes 'Starr' (Ringo Starr of the Beatles).
'exotic' indicates an anagram (an unusual form of the letters).
'buy' is an anagram of 'uby'.
'starr'+'uby'='STAR RUBY'

I've seen this clue in The Guardian.

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