L3999 course
{{Gallery |title=Model building kit for tetrahedrally bonded diatomic crystals:|width=250 | height=260 |align=center |image:Tetrahedral_kit.jpg|Model building kit for tetrahedrally bonded diatomic crystals
{{Gallery |title=Model building kit for tetrahedrally bonded diatomic crystals:|width=250 | height=260 |align=center |image:Tetrahedral_kit.jpg|Model building kit for tetrahedrally bonded diatomic crystals