Skyward Sword Eldin Volcano key pieces is essential in opening the Earth Temple, the second Temple in the Skyward Sword HD remake. You will need five key pieces to gain entrance to the Earth Temple.
Skyward Sword Eldin Volcano Key Pieces
To find the first piece, directly west of the main door is a spot you can dig, inside the dirt mound is the key piece.
The second key piece requires you to go east of the main door and walk up the staircase. A bomb flower is situated on the edge, with a crumbling wall on the ground floor just in front of Link. There is enough range in Link's throw to get the bomb flower to reach this crumbling wall, exposing another dirt mound where the second key piece is.
This third key piece is a little further out, head west of the main door. You are now met with a slope, a bomb flower, and a wooden tower at the end of the slope. Roll the bomb down the slope to blow up this tower. With the tower fallen over, a dirt mound is exposed where you can dig for the third key piece.
Northeast of the locked Earth Temple door is a cliff overlooking a vine wall. Drop down and shimmy across the ledge. Follow the path up, using each ledge to jump to the higher ledge. Once you make your way past the ledges and vine wall, hit the button to extend the bridge. Once you reach the top past all the fire and heat, you will have your fourth key piece.
The bottom of the long slide lies a tunnel leading north to a cave with a lava pool. You will see a plugged hole that a bomb flower can be thrown at, do this and the lava will fill up the area. With the lava filled in, toss another bomb at the crumbled spot. Inside this spot is the fifth and final key piece.
Best of luck in the Earth Temple!