Zircon
Zircon and Zircon General Gem Information: It should be noted strongly that Zircon and Cubic Zirconia are different minerals in chemical make-up. (There is also a Cubic Zirconia page due to the reference to Zirconia rather than our flying eyeball friend Zircon). Zircon is made from Zirconium Silicate, and is used as a diamond simulant because it bears a strong resemblance to diamonds. It is usually found in browns and greens but it can be heat treated to blue , golden, or colorless varieties of the stone. Unlike diamonds, however, Zircon is notorious because of its brittle nature.

Other Properties:
Zircon can be used as a lucky amulet for those traveling. It also helps to aid sleep, bring prosperity and promote honor and wisdom. It also helps to aid in financial success and protects the wearer from lightning.

Notations on Wearing Zircon:
Zircon is the traditional birthstone for December.

Links between Zircon and Zircon of the Dead Moon Circus:
Zircon acts as Zirconia's aid in every way, which seems to be similar to the gemstone. Zircon acts as protection and general support. Interestingly, Zircon is used to aid in sleep which could be a reference to the dream state as well. But perhaps most importantly is the name and chemical makeup similarity to Cubic Zirconia, and the fact that both gems are often poor substitutes for diamonds. This is probably a note on the fact that Nehellenia is a false queen of the moon whereas Usagi (who is represented by diamonds) is the true treasure.

References:
Zircon
Find Your Fate- Zircon