All Kinds of Crystals

Diamond is a crystal, and so are salt and sugar.

Things which are crystals are able to maintain their original shape no matter how many times they are broken up. A common misconception is that glass is a crystal. This is not true, because when glass is smashed, it breaks into totally different shapes.

How many types of crystals are there?

It all begins with a simple cube...


From the diagram above (click on it to enlarge), we see that by pushing and pulling on a simple cube, we get other possible forms of crystals. The seven crystal structures (shaded in gray) are cubic, tetragonal, orthorhombic, monoclinic, triclinic, trigonal and hexagonal.

So, the next time you eat at McDonalds', open a packet of salt and look closely. You're looking at a cubic structure!

Diagram adapted from Dr. Sohail Khan's lecture notes, Essentials of Solid State Physics.
Introductory text adapted from Dr. Abdul Halim's lecture on X-Ray Analysis.