December Birthstone Day this Saturday

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 4.4 billion years old!

2 thoughts on “December Birthstone Day this Saturday

    • 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!”

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