Element of unusual ringtone (8)
I believe the answer is:
nitrogen
'element' is the definition.
(nitrogen is a kind of element)
'unusual ringtone' is the wordplay.
'unusual' indicates an anagram.
'ringtone' anagrammed gives 'NITROGEN'.
'of' acts as a link.
(Other definitions for nitrogen that I've seen before include "creates much atmosphere" , "Major constituent of air" , "It forms the greater part of air" , "It's a gas, the strange ringtone" , "Main element of air" .)