Mix igneous rocks in fabricated mineral (9,5)

I believe the answer is:

magnesium oxide

'mineral' is the definition.
(I know that magnesium oxide is a type of mineral)

'mix igneous rocks in fabricated' is the wordplay.
'rocks' indicates an anagram.
'in' is an insertion indicator.
'fabricated' becomes 'made' (I've seen this in another clue).
'mix'+'igneous'='mixigneous'
'mixigneous' with letters rearranged gives 'gnesiumoxi'.
'gnesiumoxi' placed into 'made' is 'MAGNESIUM OXIDE'.

I've seen this clue in The Sunday Times and The Times.

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