Compressed Hydrated Coal Ball is a processing item from the IndustrialCraft 2 mod, sitting in the middle of the synthetic diamond production chain. You make it by placing a Coal Ball into a powered IC2 Compressor, which spends EU energy to squeeze the ball into its dense compressed form. The Coal Ball itself is crafted from 8 Coal Dust surrounding 1 Flint in the crafting grid, and the coal dust is hydrated with water in the versions that use the "hydrated" naming. The compressed ball has no standalone use; it is purely an ingredient. To advance toward diamonds, surround 1 Obsidian with 8 compressed balls in the crafting grid to form a Coal Chunk, then compress that chunk again in the Compressor to obtain one Industrial Diamond. Coal Dust comes from running coal through an IC2 Macerator, so the full chain of Macerator, crafting table and Compressor turns cheap, renewable coal into valuable industrial diamonds without mining. Those diamonds power advanced IndustrialCraft 2 tools, drills and machine casings.