You cannot splice CAVE DIRT. You have to buy it or acquire it otherwise. CAVE DIRT is in terrain category. You get experiance points for breaking CAVE DIRT. How many times you need to hit it? Head to the wiki for more info: <a href="https://growtopia.fandom.com/wiki/Cave_Dirt">cave dirt</a> By default you should get at least 1 seed back. Will you strike it rich? You just have to count the gems yourself. Will you get enough blocks to build something? You just have to find out yourself.