Question: Is there a crystal that's so thin that you can't see it but really really sharp?

Steven Gardner answered on 27 Jun 2013:

I don’t know of one, about the closest thing I can think of is a diamond knife.

Diamond is the hardest thing we know of, so it’s really good for making knifes to take thin slices of other materials.

To make samples to go in electron microscopes for example we embed the sample is resin and bake it till it goes hard, then we use a super sharp diamond knife to cut sections thinner than a hair. These sections are then floated onto water and picked up with a small copper grid before being dried and then put in the microscope.