Being stony, gives nothing to a friend (4)
I believe the answer is:
opal
'being stony gives nothing to a friend' is the definition.
I can't tell whether this defines the answer.
'nothing to a friend' is the wordplay.
'nothing' becomes 'o' (looks like zero - 0).
'to a friend' becomes 'pal' (pal is a kind of friend).
'o'+'pal'='OPAL'
Can you help me to learn more?
(Other definitions for opal that I've seen before include "Mineral, usually iridescent" , "Milky iridescent stone" , "Precious stone" , "Milky-white gem" , "often semi-transparent" .)