Old friends providing gems (5)
I believe the answer is:
opals
'gems' is the definition.
(opal is a kind of gem)
'old friends' is the wordplay.
'old' becomes 'o' (abbreviation).
'friends' becomes 'pals' (pal is a kind of friend).
'o'+'pals'='OPALS'
'providing' acts as a link.
(Other definitions for opals that I've seen before include "Milky-white stones" , "Milky white and coloured gems" , "Milky gemstones with delicate colours" , "Milky sparkling gemstones" , "jewels" .)