Have the students make models of the basic crystal shapes using these paper models (or if you don't have the class time to devote to this, you could make a set to have on hand when it comes time to explain crystalline structure*):
Cubic Crystal
Tetragonal Crystal
Hexagonal Crystal
Orthorhombic Crystal
Rhombohedral Crystal
Monoclinic Crystal
Triclinic Crystal
*If you're making a set for classroom use, to have on hand year after year, you might want to go to the extra effort of making your models with cardstock. They take a little more effort to fold, but they'll hold up better. Also, make sure you label your models with the crystal shapes - you may be able to remember them for a couple of days, but when you pull them out next year... :)
