Crossword Genius

Banded chalcedony used as a gemstone (5)

Ross

I believe the answer is:

agate

(Other definitions for agate that I've seen before include "Banded ornamental stone" , "marble" , "Semi-transparent stone" , "Semi-precious stone" , "Ornamental form of quartz" .)

I've seen this clue in the Sydney Morning Herald.
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