Crossword Genius

Hard form of aluminium oxide whose red variety is called ruby (8)

Ross

I believe the answer is:

corundum

(Other definitions for corundum that I've seen before include "Abrasive form of alumina" , "Stone" , "Extremely hard mineral used as an abrasive" , "Hard form of alumina" .)

I've seen this clue in The Mirror.
Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.