Abrasive English line this writer penned (5)
I believe the answer is:
emery
'abrasive' is the definition.
(emery is used as an abrasive)
'english line this writer penned' is the wordplay.
'english' becomes 'e' (abbreviation).
'line' becomes 'ry' (abbreviation for railway).
'this writer' becomes 'me' (the person who wrote the clues).
'penned' indicates putting letters inside (inserted letters are enclosed or penned in).
'e'+'ry'='ery'
'ery' placed around 'me' is 'EMERY'.
(Other definitions for emery that I've seen before include "Hard grey-black mineral used as an abrasive" , "Black abrasive" , "Abrasive material" , "Abrasive form of corundum" , "Hard black-grey mineral used in grinding and polishing" .)