Ever look closely at table salt?  If you look carefully, you will see that all the little pieces have have many flat surfaces, and some even look just like little cubes.

WHY IS THIS?

In many solids, the particles are arranged in repeating structures called crystals.  In the case of table salt, atoms of Sodium (green) and Chlorine (orange) always get together in the manner shown above.  You can't see the individual atoms, but we can tell from the crystal shape how the atoms are arranged.

Snowflakes are crystals.  Why do they always have six "spokes"?

What is one other substance that is obviously a crystal?

What is the evidence for your answer?