Stone man at a location (9)

I believe the answer is:

marcasite

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'stone' is the definition.
Both the answer and definition are singular nouns.
Perhaps there's an association between them I don't understand?

'man at a location' is the wordplay.
'man' becomes 'marc' ().
'at' says to put letters next to each other.
'location' becomes 'site' (site is a kind of location).
'marc'+'a'+'site'='MARCASITE'

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I've seen this clue in The Daily Express.

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