Crossword Genius

Turning out mineral for gemstone (10)

Ross

I believe the answer is:

tourmaline

'gemstone' is the definition.
(tourmaline is a kind of gemstone)

'turning out mineral' is the wordplay.
'turning' is an anagram indicator.
'out'+'mineral'='outmineral'
'outmineral' with letters rearranged gives 'TOURMALINE'.

'for' is the link.

(Other definitions for tourmaline that I've seen before include "Beautiful grey or black mineral" , "Beautiful blackish mineral" .)

I've seen this clue in The Telegraph.
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