Crystal Angles

Quartz crystal

How can a random assortment of molecules arrange themselves in geometric shapes with such smooth sides and precise angles?

It has to do with how the molecules fit together. Imagine a jigsaw puzzle. You start with a pile of strangely shaped pieces, but when you put them together, you wind up with a rectangular shape, with smooth sides and sharp corners. No matter how many times you take it apart and put it back together, the puzzle will always form the same shape, with the same angles at the corners.