A Mining Turtle is the same as aTurtle, only now you can use it to mine for you. Mining a block is done instantly, and will only retrieve items or blocks if mining the block with the same pick would drop items or blocks normally, so any mining turtle can mine obsidian (instantly), but only a turtle with a diamond pick will retrieve ablock of obsidian; a turtle with a Ruby pick will not (however both can still mine Logs and Dirt)). The turtle still requires fuel to move, but mining a block (without moving) does not require fuel. The pickaxe does not have a durability - it can be used infinitely.
Since it mines every mineable block at the same speed, the mining turtle is also very useful for quickly mining obsidian, as long as you're familiar with the controls.
'BUT BE WARNED! USING TOO MANY MINING TURTLES IN THE SAME C'HUNK CAN CAUSE SERV'ER'S OR YOUR OWN SINGLE PLAYER WORLD TO LAG OR TO CRASH!