Jewel in ring given to a friend (4)
I believe the answer is:
opal
'jewel' is the definition.
(I've seen this before)
'ring given to a friend' is the wordplay.
'ring' becomes 'O' (letter resembling a ring).
'given to' means one lot of letters go next to another.
'a friend' becomes 'pal' (pal can mean a friend).
'o'+'pal'='OPAL'
'in' is the link.
(Other definitions for opal that I've seen before include "One in a ring perhaps" , "Mineral, usually iridescent" , "Form of hydrated silica, often used as a gemstone" , "Shimmering stone" , "Gem stone" .)