Old lady bites edges off stone (7)
I believe the answer is:
granite
'stone' is the definition.
(I know that granite is a type of batholite)
'old lady bites edges' is the wordplay.
'old lady' becomes 'gran' (short for grandmother).
'bites edges' becomes 'ite' (I can't justify this - if you can you should believe this answer much more).
'gran'+'ite'='GRANITE'
'off' acts as a link.
Can you help me to learn more?
(Other definitions for granite that I've seen before include "Igneous rock, generally composed of feldspar and mica and quartz" , "Coarse-grained igneous rock" , "Hard granular rock" , "determination" , "Get rain (anag) - rock" .)