This is a diamond chest and a gold to diamond upgrade. Both are from the Iron Chest mod. The diamond chest is essentially a chest that can store much more items than a regular chest, while the upgrade upgrades a preexisting gold chest to a diamond one.

Iron Chests mod download= http://minecraft.curseforge.com/projects/iron-chests/files

Iron Chests information on Feed the Beast wikia= http://feed-the-beast.wikia.com/wiki/Iron_Chests

Note: Sorry if the chest in the photo looks bad, I'm still transitioning from tape to glue. Also, if you don't understand what I mean by put onto back piece, there is a photo.