Ring mate to get a stone (4)
I believe the answer is:
opal
'a stone' is the definition.
(gemstone)
'ring mate' is the wordplay.
'ring' becomes 'O' (letter resembling a ring).
'mate' becomes 'pal' (I've seen this before).
'o'+'pal'='OPAL'
'to get' is the link.
(Other definitions for opal that I've seen before include "Iridescent gemstone" , "Iridescent quartz-like stone" , "Quartz-like gemstone" , "Milky stuff that's hard" , "Type of gemstone" .)