Main charity served up something sparkling (6)
I believe the answer is:
diadem
'something sparkling' is the definition.
'main charity served up' is the wordplay.
'main' becomes 'med' ('main' can mean the sea - eg Mediterranean or Med).
'charity' becomes 'aid' (I've seen this before).
'served up' shows that the letters should be reversed in order.
'med'+'aid'='medaid'
'medaid' in reverse letter order is 'DIADEM'.
(Other definitions for diadem that I've seen before include "Ornamental jewelled headdress" , "A crowning glory" , "Crown or similar adornment" , "Small jewelled crown" , "Crown or headband worn as symbol of sovereignty" .)