Sparkling old friend with energy and fragrance (10)
I believe the answer is:
opalescent
'sparkling' is the definition.
(I've seen this before)
'old friend with energy and fragrance' is the wordplay.
'old friend' becomes 'opal' (I can't explain this - if you can you should believe this answer much more).
'with' says to put letters next to each other.
'energy' becomes 'e' (physics symbol as in E=mcp).
'and' says to put letters next to each other.
'fragrance' becomes 'scent' (synonyms).
'opal'+'e'+'scent'='OPALESCENT'
(Other definitions for opalescent that I've seen before include "Shot" , "Sparkling" , "shimmering" .)