This Saturday is Birthstone Day for December. That means free museum admission for anyone born in the month of December!
Cathodoluminescence image of a zircon crystal from Jack Hills. Photo: John Valley, University of Wisconsin
December babies, your birthstone is zircon. Forget diamonds: zircons are truly forever. The oldest known minerals in Earth’s crust are zircons from Jack Hills in Australia. They have been dated to 4.4Â billion years old!
That is a beautiful stone. Are they made under pressure, volcanic? That’s amazing. Wish it was my birthday month.
Zircons can be made in both igneous and metamorphic rocks. What’s amazing is that they can be “recycled.” A zircon that crystallizes from a magma may one day be buried deeply and then resume growing due to metamorphic reactions, creating a new outside layer. Or it can end up in a magma again, and instead of melting it will grow another layer or two. The photo you see is a slice through a single grain. The complex core shows that this zircon has a complicated growth history and was involved in more than one geologic “event!”