Wherein my illusions are dashed

Andy Brunning presents an infographic of the Mohs Hardness Scale, something I learned about when I was a squirt and received a student’s geology kit and have subsequently forgotten about. But behind that tidy 0-to-10 scale is a dirty little secret:

There’s no fixed value of hardness between the different numbers in the scale — in fact, diamond at 10 is several times harder than corundum at 9, but corundum is only around twice as hard as topaz at 8.