In a find unlike anything seen before, a piece of opal from the island of Java in Indonesia holds some remarkable cargo: a stunningly preserved insect that may be at least four to seven million years old.

Previously, plenty of ancient insects have been found in amber, a gemstone made of fossilized tree resin. When animals became encased in the fresh resin, it entombs them rapidly enough to preserve the remains, often with exquisite detail. (See a dinosaur-era bird found preserved in amber.)

But typically, the natural formation of opal involves silica solutions concentrating in cavities underground over thousands or even millions of years, raising questions as to how an insect could have been preserved in this way.

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“It’s an incredibly unlikely object—but so are many other rare and wondrous things in nature that were thought not to exist, or be theoretically possible, until they were shown to be true,” comments Jenni Brammall, an expert on opal and opalized fossils at the Australian Opal Centre in Lightning Ridge, New South Wales.

The sample is currently in private hands and has yet to be thoroughly studied by paleontologists or geochemists. But if it's confirmed, the discovery may not only represent a previously unknown source of valuable fossils, it may change what we know about a popular gemstone.

Brammall has known of the specimen since 2017 and has also seen images of a second possible insect in opal from the same mine in Java. However, because she has only seen photos and no scientific research has yet been published, she says it's difficult for her to offer an informed opinion on the sample.

“I have no reason to doubt that it’s genuine, other than that it is so unlikely, but we’ll have to wait and see what the science says," Brammall says. “I hope it’s genuine, because if it is, it’s going to reveal some absolutely fascinating things about opal formation.”

Filling voids

A Javanese opal seller found the odd specimen in 2015, and it passed through several hands before being bought by Brian T. Berger, a gemologist and dealer in Philadelphia, Pennsylvania. Berger himself was initially skeptical that the specimen was real, so he submitted it for analysis to the Gemological Institute of America (GIA). Experts there confirmed with National Geographic that they believe the specimen to be authentic natural opal that has not been tampered with.

"I was thinking this has to be a counterfeit," Berger says. "This is some kind of new treatment or something, but I studied the stone, and everything looked right… and the GIA confirmed the findings." Berger has since written about the specimen in a blog post for Entomology Today.

Numerous opal fossils have been found in Lighting Ridge in Australia, although the process there is different. These "replacement" fossils formed when spaces in the ground once occupied by bones and teeth were filled with silica solution that turned to opal, like jelly in a mold. Phil Bell, a paleontologist at the University of New England in Armidale, Australia, recently described a new species of dinosaur from fossil fragments opalized in this manner.

“Opalized fossils have undoubtedly gone through millions of years of history underground, being squashed, heated up, and all the rest of it,” he says. While it’s not impossible, he’s skeptical that an insect could be preserved in the same way.

Instead, Berger and a number of experts think it's possible the specimen is made of amber that somehow became opalized.

“My gut reaction is that it looks like a piece of amber secondarily embedded in opal,” comments Ryan McKeller, who researches fossils in amber at the Royal Saskatchewan Museum in Regina, Canada. Opalized fossil wood is common from Java, hinting at a possible route for tree resin to have become embedded in opal.

“Opal usually fills voids,” McKeller says. “In this sort of scenario, a log might have been opalized, leaving its amber content encased.” A known specimen of Canadian amber filled a crack in a piece of wood and was subsequently turned into silica on the outside, he says.

“The new specimen may have undergone a similar process, but it is pretty speculative until chemical analyses are conducted and researchers take a hard look at preservation of the insect.”

Awaiting analysis

Until the sample goes through full scientific analysis, many experts were also unwilling to venture a guess as to the kind of insect trapped inside.

Given the shriveled appearance of the wings, it may represent an adult form of a winged insect recently emerged from its pupal stage, says Ricardo Pérez-de la Fuente, a paleoentomologist at the Oxford University Museum of Natural History in the U.K. But he emphasizes that it is vital the insect is formally studied before anyone can offer “sufficiently credible arguments" about its biology.

Thomas van de Kamp, an entomologist at the Karlsruhe Institute of Technology in Germany, is one of the experts hoping to study it. He wants to use a synchrotron to do a detailed x-ray scan and create a 3-D reconstruction that will offer a comprehensive description of the animal.

Many of the known fossil insects were found in amber and so are probably tree-living species. If the newfound specimen formed in opal alone, it may represent a rare glimpse at a creature from a different kind of environment.

“Other types of 3-D preverved insects are therefore extremely valuable to extend our view,” van de Kamp says.

Berger says that he is currently in talks with museum experts and other researchers around the world on how to collaborate on scientific study of the sample. After that, he says, he’d like the specimen to be displayed at a museum.

“I might sell it to a museum, I might donate it, I might keep it and just loan it for display purposes," he says. "I haven’t really decided.”