Transparent mineral (7)
I believe the answer is:
crystal
'transparent mineral' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for crystal that I've seen before include "The fortune teller may use a . . . . . . . ball" , "Type of clear-cut, lucent glass" , "Glass made at Waterford" , "Regular-shaped mineral piece" , "Highly transparent glass" .)