What is the difference between cubic zirconia & zircon?

Cubic Zirconia

Cubic zirconia is a synthetic cubic crystalline form of zirconium dioxide. (Um, ok then!)

What it actually is, is a manufactured crystal, made to resemble Zircon, which is a natural semi-precious gemstone.

Unfortunately, cubic zirconia is often erroneously abbreviated to zircon, but zircon is much more expensive. If a $20 ring says it has a zircon stone, it does not! If a $200 ring says it does, it probably is. 

We don't currently have anything that has zircon in it, due to it's high price.

An interesting little fact is that Zircon is the stone we were able to obtain the age of the Earth from, it being the oldest rock at 4.3 billion years old, to be carbon-dated in the Earth's crust.