Instrument made of wood splitting stone (6)
I believe the answer is:
spinet
'instrument' is the definition.
(spinet is a historical type of musical instrument)
'wood splitting stone' is the wordplay.
'wood' becomes 'pine' (pine is a kind of wood).
'splitting' is an insertion indicator.
'stone' becomes 'st'.
'pine' placed into 'st' is 'SPINET'.
'made of' acts as a link.
(Other definitions for spinet that I've seen before include "Instrument resembling a small harpsichord" , "organ" , "A small harpsichord of old" , "Type of early harpsichord" , "Instep (anag)" .)