Leaves are a very common block in Mine Blocks because they can be found on trees. When they are mined, they have a chance of dropping saplings. Saplings can be used to replant trees. Some leaves contain apples, lemons and oranges, making them an easy source of food.
The only way to obtain this block to place is to use shears.
When source wood blocks are removed, the leaves blocks will decay or disappear, dropping any fruit they may have contained or occasionally saplings.