When we tested hardness, we were trying to scratch the specimen, not break it. For the next two tests, fracture and cleavage, we will be breaking the specimens. We are not looking at how difficult it is to break them. Instead, we will be looking at how they break, especially at the shape of those broken surfaces. Minerals that break in flat, smooth planes have a property called cleavage, and we will look at those in the next test. Any kind of break that is not cleavage is called fracture, and there are several different kinds.

This experiment involves balancing a hammer, a ruler, and some string. It is one of those balancing tricks that seem as though they just should not work, even though you understand the science behind them. I first learned it when I was eight years old, but it is still one of my favorites.