It varies. You are right that some are harder than pure sapphire, but it depends on the exact grade, etc, and depends on what you do to the sapphire. Suffice

It varies. You are right that some are harder than pure sapphire, but it depends on the exact grade, etc, and depends on what you do to the sapphire. Suffice to say: I have tested saw blades i have against sapphire screened watches i have. They do not scratch. ¯\_(ツ)_/¯