The Mohs hardness scale divides minerals into 10 levels of hardness, with a designated mineral for each level. The stone to be tested is rubbed against these minerals and the scale determines the level of wear observed by the mineral that scrapes it.
When you hear the word "hardness tester," you might imagine it to be some kind of electronic device, but it's actually made up of 10 index stones. In a world filled with electronic devices that make our lives easier, I think this is a truly human tool. I doubt you'll ever have a chance to use it, though.
Mohs hardness scale
We have also uploaded fossil and mineral specimens that were used in junior high school classes.
plant fossil specimens
igneous rock specimen
Sedimentary rock specimens
mineral specimens