Stone ring, intimate (4)
I believe the answer is:
opal
'stone' is the definition.
(gemstone)
'ring intimate' is the wordplay.
'ring' becomes 'O' (letter resembling a ring).
'intimate' becomes 'pal' (both can mean a friend).
'o'+'pal'='OPAL'
(Other definitions for opal that I've seen before include "Precious stone" , "Mineral, usually iridescent" , "Semi-precious stone of b;uish white colour" , "Milky-white mineral" , "raw material" .)