Abrasive former student one's interrupted (7)
I believe the answer is:
alumina
'abrasive' is the definition.
(alumina can be used as an abrasive)
'former student one's interrupted' is the wordplay.
'former student' becomes 'alumna' (female former student).
'one' becomes 'I' (Roman numeral).
'interrupted' is an insertion indicator.
'alumna' enclosing 'i' is 'ALUMINA'.
(Other definitions for alumina that I've seen before include "Substance of sapphire" , "Metal oxide found in many clays" , "Metallic oxide that is a constituent of many clays" , "emery" , "Oxide in corundum" .)