Since Alpha 0.0.9e you can't get it from the altar; instead you can find a something like a shrine near the mine (to the left of it) where you have to put the Embossed Copper Sword with Uncommon Golden Grip and a Common Hero Guard. Behind the slot you put the sword in, there are three unlit crystals. Upon attempting to insert a sword into the shrine, 1 or more of the crystals will light up, the number corresponding with how many of the three pieces of the sword are correct. For example, inserting a sword with the Uncommon Grip and V2 One Hand Guard, but a Normal Blade will result in 2 of the crystals lighting up. Once you insert a sword with all 3 parts correct, all 3 crystals will light up and the Earth Crystal will appear above the shrine.