Originally Posted by
Panthers007
Alumina has a hardness of 9 on the Moh's scale. Diamond's are 10..... In this form it is also made synthetically and called Carborundum.
Two points:
1. The Moh hardness scale is non-linear and the difference between a Moh of 9 and a Moh of 10 is huge.
2. Carborundum isn't alumina, its silicon carbide.