Crossword Genius

Black stone (4)

Ross

I believe the answer is:

onyx

'black stone' is the definition.
(I've seen this in another clue)

This is the entire clue.

(Other definitions for onyx that I've seen before include "material for making cameos" , "Cameo material" , "Stone-like marble with layered colours" , "Black variety of quartz" , "Marble-like gemstone" .)

I've seen this clue in the Penny Press and the LA Times.
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