Ancient stone vessel found in metal wrapping (6)
I believe the answer is:
fossil
'ancient stone' is the definition.
(I've seen this before)
'vessel found in metal wrapping' is the wordplay.
'vessel' becomes 'SS' (short for steamship).
'found in' means one lot of letters goes inside another.
'metal wrapping' becomes 'foil' (I can't justify this - if you can you should believe this answer much more).
'ss' going within 'foil' is 'FOSSIL'.
Can you help me to learn more?
(Other definitions for fossil that I've seen before include "Petrified remains of plant or animal" , "Remains or impression of a prehistoric plant or animal" , "Antiquated person" , "amber, say" , "This fuel is natural, extracted from the ground" .)