The Crystal Chest is a storage compartment from the Iron Chests mod. It has the same inventory space as the Diamond Chest with 108 slots, but allows the visualization of stored items. It will show the eight most numerous items stored within.
A Diamond Chest can be upgraded to a Crystal Chest using a Diamond to Crystal Chest Upgrade. It is crafted with eight Glass and one Obsidian. Apply the upgrade by right-clicking on the Diamond Chest with the upgrade in hand.