Possibly rocky piece of furniture (3)

I believe the answer is:
bed
This clue could be a double definition.
'possibly rocky piece' is the first definition.
'bed' can be an answer for 'piece' (I have seen 'Piece of furniture ' mean 'bed' so perhaps 'piece' could also mean 'bed'). I'm unsure of the 'possibly rocky' bit.
'furniture' is the second definition.
(bed is a kind of furniture)
'of' acts as a link.
Can you help me to learn more?
(Other definitions for bed that I've seen before include "Bottom < layer" , "Divan" , "Firmly settle" , "Matrimonial duties" , "For sleep and flowers" .)
