Which rocks will scratch a steel knife or window glass?

Rocks that can scratch a steel knife or window glass typically have a hardness of 5.5 or higher on the Mohs scale. Examples include quartz, which has a hardness of 7, and topaz, with a hardness of 8. Other harder minerals like corundum (hardness of 9) and diamond (hardness of 10) can also scratch both steel and glass. Generally, any rock containing these minerals can potentially scratch a steel knife or window glass.