Etherium Pickaxe
Classic of all classics.
It can be created in a Crafting Table, via shaped recipe:
When mining a block that pickaxe is effective on, it will break additional such blocks in 3x3x1 area centered around the broken block, orientated respectively to the player's sight. This effect will not trigger if they are holding Shift, however, allowing to mine individual blocks if it's required.
Etherium Pickaxe has a harvest level of 4, which usually means that it can harvest any blocks Diamond Pickaxe can. It also has 3000 points of durability and slightly faster breaking speed, similar to other tools made of Etherium.