Table salt. Formula: NaCl
Table salt is probably the most available component for growing crystals. It is also one of the hardest components to grow. I made countless number of attempts, and only one of them produced fine results, presented here. You are lucky if you can get clear, well-formed 5mm, salt crystal. If you get 10mm, it is success. And if you manage to get a bigger one, then please tell me how you did it.