More important, uranium and guide can shift around inside of a crystal, or even escape or enter the zircon. This mobility can toss off the guide isotope rely accustomed to estimate the zircon ages, which is the source of the decades-long controversy over the Jack Hills zircons' Methuselah lifespan. Colorless https://www.gemsbiz.com/blog/explore/the-december-birthstone-zircon-tanzanite-turquoise