default: flowing lava can cool down to basalt

mods/default/functions.lua

@@ -100,11 +100,16 @@ end
 -- Lavacooling
 --
 
+lavagen = {
+"darkage:basalt",
+"default:stone"
+}
+
 default.cool_lava = function(pos, node)
 	if node.name == "default:lava_source" then
 		minetest.set_node(pos, {name = "default:obsidian"})
-	else -- Lava flowing
-		minetest.set_node(pos, {name = "default:stone"})
+    else
+        minetest.set_node(pos, {name = lavagen[math.random(1,#lavagen)]}) 
 	end
 	minetest.sound_play("default_cool_lava",
 		{pos = pos, max_hear_distance = 16, gain = 0.25})