Stone circle left on peak, oddly (4)

I believe the answer is:

opal

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'stone' is the definition.
(thesaurus)

'circle left on peak oddly' is the wordplay.
'circle' becomes 'lap' ('lap' can be a synonym of 'circle').
'left' is a reversal indicator.
'on' says to put letters next to each other.
'peak oddly' becomes 'o' (I am not sure about this - if you are sure you should believe this answer much more).
'lap' reversed gives 'pal'.
'pal' after 'o' is 'OPAL'.

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(Other definitions for opal that I've seen before include "raw material" , "Milky white gem" , "Delicately coloured gem" , "Semi-transparent gemstone" , "Opaque gem" .)

I've seen this clue in The Telegraph.

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