minetest.register_ore({
	ore_type       = "sheet",
	ore            = "myconcrete:limestone",
	wherein        = "stone",
	clust_scarcity = 60*60*60,
	clust_num_ores = 30,
	clust_size     = 3,
	height_min     = -31000,
	height_max     = -50,
})