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Glass Insects

Remarkable insect fossils in the Invertebrate Paleontology collections

This immature dragonfly fossil from California’s Calico Mountains is a “glass” insect — the result of an interesting fossilization process called silicification (which is also quite the tongue-twister). Photo by Deniz Durmus.


Walking through row after row of cabinets in the Invertebrate Paleontology collections, you can see all kinds of amazing fossils, like clam shells from the Ice Age and strange creatures like trilobites that lived hundreds of millions of years ago. But some fossils in this vast collection are particularly eye-catching because they look like little glass figurines of insects.

a photo of small containers of insect fossils that look like glass figurines next to small blobs of sediment
These “glass” insects were recovered from concretions like the one-inch-long ones to the right — little packets of sediment that hold a fossil within them.

Here’s how it happened: when these insects died about 14 million years ago, their bodies decomposed in an ancient lake. Eventually they got enveloped in rock, and the insects’ bodies were replaced by minerals like quartz (also known as silica, which is why this process is called silicification). The resulting fossils have a translucent, glass-like appearance.

When paleontologists (people who study fossils) find these fossils, they’re contained in little blobs of sediment called “concretions.” To expose the delicate insect fossil inside, these concretions are dropped in a weak acid bath, which eats away at the surrounding material but leaves the quartz and other minerals intact. Once the surrounding sediment has dissolved away, you are left with a spectacular glassy fossil insect.

This kind of preservation is exceptionally rare, and it’s as scientifically valuable as it is fun to look at. Notice the level of detail in these fossils — structures of the wings and legs are still visible. Even microscopic features like eye facets and individual hairs can be preserved this way. This means that paleontologists can learn a lot about these animals from so long ago. Just be really careful with them — they’re extremely breakable!



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