A rolling stone (6)
I believe the answer is:
marble
This clue could be a double definition.
'a rolling' is the first definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.
'stone' is the second definition.
(I know that marble is a type of stone)
Can you help me to learn more?
(Other definitions for marble that I've seen before include "Crystalline limestone often used by sculptors" , "Hard crystalline limestone, can be polished" , "Hard crystalline limestone used for sculpture" , "Crystallised limestone" , "Hard crystalline metamorphic rock" .)