Splice LAVA and CAVE BACKGROUND to make LAVA ROCK. You can find this item in building category. This seed grows fast, less than 1 minute. You get experiance points for breaking LAVA ROCK. Hitting it will break it but you need to count the hits yourself. By default you should get at least 1 seed back. Profiting with this might be questionable. Will you get enough blocks to build something? You just have to find out yourself.