Gem of Eternal Density (Equivalent Exchange)

Finally, the Gem of Eternal Density is a versatile relic that condenses your inventory using the Equivalent Exchange Formulas common to the Philosopher's Stone. As you mine, depending on what level you have your Gem charged to, it will condense them down to a more compact form. The Gem is always free to use.
Level 0 - Condenses dirt, sand, clay, flint, sandstone and gravel into cobblestone.
Level 1 - Condenses stone, cobblestone and netherrack into redstone ore. Condenses redstone ore immediately into iron. Also condenses coal and charcoal into glowstone dust, to fuel your alchemy as you mine. Lastly, condenses glass into pure ice blocks.
Level 2 - Condenses iron ore into gold ore. Condenses lapis lazuli and obsidian ore into lapis lazuli ore blocks.
Level 3 (maximum) - Condenses gold ore into diamond ore, condenses lapis lazuli ore into pure diamonds.
It will try and leave a stack of dirt, cobblestone and/or netherrack in your inventory so you can still use your Philosopher's stone if you're in a bind.
In order for the Gem to work, you must first activate it with the G key, or whatever you have set to toggle active items.
New in 3.4, the gem can be charged (or uncharged, it will function at level 0) and added to an alchemical chest - it will not work on normal chests.. while within said chest, it will function on that inventory. It does not need to be activated to work in an alchemical chest.