Quartz is corroded by silver (5)
I believe the answer is:
agate
'quartz' is the definition.
(agate is a kind of quartz)
'corroded by silver' is the wordplay.
'corroded' becomes 'ate' ('eat' can be a synonym of 'corrode').
'by' means one lot of letters go next to another.
'silver' becomes 'ag' (Ag is the chemical symbol for silver).
'ate' after 'ag' is 'AGATE'.
'is' is the link.
(Other definitions for agate that I've seen before include "Quartz with bands of colour, used in jewellery" , "Striped stone" , "Onyx" , "Precious stone" , "Semi-precious stone" .)