Gemstone in ring presented to friend (4)
I believe the answer is:
opal
'gemstone' is the definition.
(opal is a kind of gemstone)
'ring presented to friend' is the wordplay.
'ring' becomes 'o'.
'presented to' means one lot of letters go next to another.
'friend' becomes 'pal' (pal is a kind of friend).
'o'+'pal'='OPAL'
'in' acts as a link.
(Other definitions for opal that I've seen before include "Birthstone for October" , "Delicately-coloured gem" , "Type of gemstone" , "Semi-precious stone of milky or bluish colour" , "it may be highly valued" .)