My buddy Jake thought his kitchen countertop was granite until he tested it with a quartz sample. Left a huge scratch right down the middle, his wife was not happy.
My quartz countertop at the old apartment taught me the same lesson. I tried to scratch it with a regular kitchen knife just to see, and it didn't leave a single mark. That's when I finally understood the whole Mohs scale thing for real. Have you tried testing any other materials around your house?
At Lincoln High, our chem lab used Mohs kits for mineral tests. Kitchen knives can have different steel hardness, so not scratching quartz might not prove much. I saw a cheap knife leave a mark on my cousin's quartz countertop. The scale works best with standard tools, not random objects. Home tests can be misleading if you don't know the knife's hardness. That's why I see the knife test as incomplete.