Strange layer inside with iodine and another element (7)
I believe the answer is:
rhenium
'element' is the definition.
(I know that rhenium is a type of metal)
'strange layer inside with iodine' is the wordplay.
'strange' becomes 'rum' (similar in meaning).
'layer' becomes 'hen' (something which lays - eggs in this case).
'inside' is an insertion indicator.
'with' means one lot of letters goes inside another.
'iodine' becomes 'I' (chemical symbol).
'rum' enclosing 'hen' is 'rhenum'.
'rhenum' enclosing 'i' is 'RHENIUM'.
'and another' acts as a link.
(Other definitions for rhenium that I've seen before include "Chemical" , "Metal" , "Element (Re)" .)