Clear quartz (7)

I believe the answer is:

crystal

'clear quartz' is the definition.
(I've seen this before)

This is the entire clue.

(Other definitions for crystal that I've seen before include "Globe for the fortune-teller" , "Type of clear-cut, lucent glass" , "The fortune teller may use a . . . . . . . ball" , "Quality glass" , "Quartz, for example" .)

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

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