Unusual planet revealing some elements (4,5)
I believe the answer is:
rare earth
'some elements' is the definition.
(rare-earth element is a kind of element)
'unusual planet' is the wordplay.
'unusual' becomes 'rare' (rare can mean unusual or odd).
'planet' becomes 'earth' (Earth is an example).
'rare'+'earth'='RARE-EARTH'
'revealing' acts as a link.
(Other definitions for rare earth that I've seen before include "One of a particular group of metallic elements" , "Particular element" , "Metal" , "element such as promethium" , "One of a group of 15 hard to distinguish elements - at her rear (anag)" .)