Emerald Shards and Pieces are added in from the LegendGear mod. They are the shattered remains of Emeralds, and can be obtained in a large variety of ways. While useless in Shard or Piece form, you can craft them back into a full Emerald in order to trade with NPCs or for use in recipes. With the addition of this mod, you now hear distinctive sounds when you pick up any Emerald Shards, Pieces, or even Emeralds themselves. This sound also plays when you use 8 of any Shard or Piece to craft a Piece/Emerald, respectively.
Emerald Shards can be crafted into Emerald Pieces by right clicking with 8 of them in your hand. Similarly, 8 Emerald Pieces can be right clicked to create a vanilla Emerald, meaning it costs a total of 64 Emerald Shards to create a single vanilla Emerald. You can take 9 Emeralds and turn it into a Block of Emerald, using 576 total shards to make the block.
You can reverse-engineer Emeralds into Pieces, and Pieces into Shards by placing an Emerald/Emerald Piece (respectively) onto a crafting table. This is rarely useful, except in the case of very limited inventory space (if you are able to contain all the Emerald Pieces/Shards in a single slot), or if you are doing player-to-player trading online.
Eight emerald shards can be right-clicked into one emerald piece, and 8 emerald pieces can be right clicked into an emerald as shown in the picture to the right.
Emerald Shards are sometimes dropped upon the death of a mob as well as upon destroying the top layer of a Mystic Shrub. In addition to Emerald Shards, you may also find Emerald Pieces when breaking an Energized Mystic Shrub, or very rarely, a full Emerald.