Possibly question our ersatz gemstone (4,6)

I believe the answer is:

rose quartz

'gemstone' is the definition.
(rose quartz is a kind of gemstone)

'possibly question our ersatz' is the wordplay.
'possibly' indicates an anagram.
'question' becomes 'q'.
'q'+'our'+'ersatz'='qourersatz'
'qourersatz' anagrammed gives 'ROSE QUARTZ'.

(Another definition for rose quartz that I've seen is " sort of mineral".)

I've seen this clue in The Times.

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