Crossword Genius

Semi-precious stone (3)

Ross

I think it could be either:

Which length description are you looking for?:

3

5

(Other definitions for jet that I've seen before include "Black; spurt" , "Black variety of lignite, used for ornaments" , "Spurt; aircraft" , "Rush" , "Deep black" .)

I've seen this clue in The Mirror.
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