Material for pencils Greek character put in jar (8)
I believe the answer is:
graphite
'material for pencils greek' is the definition.
I can't judge whether this defines the answer.
'character put in jar' is the wordplay.
'character' becomes 'phi' (phi is a kind of character).
'put in' indicates putting letters inside.
'jar' becomes 'grate' (make unpleasant sound).
'phi' put inside 'grate' is 'GRAPHITE'.
Can you help me to learn more?
(Other definitions for graphite that I've seen before include "black stuff" , "Mixed with clay it forms the 'lead' in pencils" , "Pencil-lead carbon" , "Writing material" , "Black carbon used in lead pencils" .)