Because the Prismarine block requires 4 shards to craft, and the Prismarine Bricks block requires 9 shards, any mod allowing Prismarine Bricks to be converted into shards (for example, Thermal Expansion's Factorizer) along with Chisel will create a method for Prismarine Shard duplication where 4 shards can be crafted into a Prismarine block, chiseled into Prismarine Bricks and then converted into 9 shards for free.