Make A Coal Crystal Garden

I remember doing this as a child. My grandparents had a furnace that burned coal so it was ready available. You can also use a charcoal briquette or stones or small pieces of brick.
They are amazing to watch grow and young children are usually quite excited about them. Be sure to have adult supervision if children are making them as they do use amonia.

CRYSTAL GARDEN: 6 tablespoons salt, 6 tablespoons liquid bluing (see Note), 6 tablespoons water, 1 tablespoon ammonia, Food coloring (optional). Combine salt, bluing, water and ammonia. Pour over small pieces of rock or coal in a shallow glass or china bowl. Drip food coloring on top, if desired. Crystals will begin to grow soon. Add water occasionally to keep crystals growing. You'll probably want to place dish on a tray or wooden board as crystals grow over the sides of the bowl. Note: Liquid bluing can be found in most markets in with the laundry soaps and products. The most popular brand is Mrs. Stewart's Liquid Bluing and is used as a laundry whitener.