The Zircon is a new gem that was added in the 6.0 update. It can be obtained from mining Zircon Ore in the Mining World, and is a semi-rare ore. It currently, along with the other gems has no real use, but will be used in the future.
Although there are no crafting uses, Zircon is a good source for EXP. To turn the Zircon into EXP, you need to put it through a Disenchanter; from which you will get a Stored Experience potion of 9.142 EXP