Zircon

Zircon is a silicate mineral. It is found in many different places in almost all kinds of rock. The chemical it is made up of is called  zirconium silicate:  ZrSiO4. Clear zircon may look like diamond and has been used as a cheaper replacement for diamond.  It is not the same as cubic zirconia, which is man-made zirconium dioxide.  In the United States, zircon is considered to be the birth stone for the month of December.

 Long lasting zircons 
Zircon is very durable. It is hard and has a high melting point of around . Therefore it has survived for a very long time, even through metamorphic very warm processes deep underground, which otherwise melts or converts normal rocks.

Zircons from the Jack Hills in the Narryer Gneiss Terrane, Yilgarn Craton, Western Australia, have yielded U–Pb (uranium–lead radioactive dating) ages up to 4.404 billion years. This is judged to be the age of crystallization, making them the oldest minerals so far dated on Earth. In addition, the oxygen isotopic compositions of some of these zircons indicate that more than 4.4 billion years ago there was already water on the surface of the Earth. This interpretation is supported by additional trace element data, but is also the subject of debate.

 References 

Category:Gemstones
Category:Nesosilicates