The most common and most likely answer to this crossword clue is the 4 letter word BORT
B
O
R
T
Buddy explains!
The straight part
We know that "Abrasive" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case abrasive = bort.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does BORT mean?
BORT noun- Poor-quality diamond, used for industrial cutting or abrasion; a poorly crystallized diamond.