It is considered the holy grail of high pressure physics that made headlines around the globe last month, and now it has suddenly disappeared from the lab in which it was born. The only known sample in the world of metallic hydrogen has vanished, and its creators have no idea what happened to it.

It’s been about a century since metallic hydrogen was first theorized, but it wasn’t until last month when Harvard scientists managed to create the incredibly rare material: hydrogen in its metallic form. Some expressed skepticism at the claim, but the scientists insisted that they’d achieved something that had never been done before.

The metallic hydrogen was being stored at 80 Kelvin and was sandwiched between two diamonds to be kept at incredibly high temperatures. However, a problem in the lab caused the diamonds to break and the metallic hydrogen suddenly disappeared. It was quite small, at 10 micrometers in diameter, so it’s possible that it’s simply missing, but it’s also possible that when the diamond vice broke, it simple turned back into a gas, according to various reports.

Harvard said in a statement when it was first reported: “The material – atomic metallic hydrogen – was created by Thomas D. Cabot Professor of the Natural Sciences Isaac Silvera and post-doctoral fellow Ranga Dias. In addition to helping scientists answer fundamental questions about the nature of matter, the material is theorized to have a wide range of applications, including as a room-temperature superconductor. The creation of the rare material is described in a January 26 paper published in Science.”