Magic Growing Rocks on wikipedia.org
A kit of mysterious rocklike objects and a clear liquid. You had to supply your own container (mine was an egg shaped jar) drop the rocks in and pour the liquid in. At least I think that was the procedure...Then you'd wait and the rocks would grow into tall, brightly colored, mountain spikes. I had that jar for years until it got icky. Never knew what the chemical compounds were responsible for making those things, but always assumed they were horribly toxic...