Crossword Genius

Oil-producing rock (5)

Ross

I believe the answer is:

shale

'oil-producing rock' is the definition.
(I've seen this in another clue)

This is all the clue.

(Other definitions for shale that I've seen before include "Clayey rock" , "Easily-split sedimentary rock" , "Oil-rich rock" , "Fine pieces of stone on leash" , "Oil-bearing rock" .)

I've seen this clue in the Penny Press.
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