[MOD] Let me mod that for you: "Compressed Coal" = Diamond

It's a start - 3x3 coal in the crafting grid = 1 diamond.

Edit: I've updated the mod to version 1.1! I've added the coal block, which is crafted using a 3x3 grid of coal. These blocks are placeable, and, when destroyed, yield your original 9 coal (they can, therefore, be used as a more effective method of storage). Also, these blocks can make 1 diamond if they are placed in a 2x2 grid.

Edit: Ok, now I feel as if we're getting somewhere. Here's the new steps (version 1.2):

• Coal Blocks are crafted in the same way as before: 3x3 grid of coal.
• Place Coal Blocks in a 2x2 grid to get a Compressed Coal Block.
• Place those in a 2x2 grid to get a Diamond.
• Compressed Coal Blocks yield 4 Coal Blocks upon breaking - Coal Blocks yield 9 coal when broken.
• The coal blocks can now be used as fuel. Compressed Coal Block lasts 16x as long as coal, the Coal Block lasts 4x as long.

Original thread

Download (Haven't tested compatibility with other mods yet, back up your minecraft.jar!)