Measure the length in millimeters. Find the area to determine which one is biggest. Record the results on your chart. A crystal is a solid form of a substance or mixture that has a repeating internal arrangement of its atoms. Crystals join together and make what's called a formation.
All crystals have a definite shape.
For crystals to form, they need time and freedom. Sometimes an atom that doesn't match that of all the other atoms while forming a crystal gets mixed in with them. This is called a stowaway atom. It could be of a different color, or size. Some gems are different colors because their molecules are different colors.