When NASA’s Perseverance rover used its laser to separate some pale rocks found in Jezero Crater in 2025, scientists weren’t expecting anything out of the ordinary. Little did they know what awaited them. The rocks contained something never before found on Mars: a mineral that, here on Earth, can be a literal treasure. The mineral was corundum, the crystalline material that forms rubies and sapphires. And there was even a smell of chrome, which gives rubies their distinctive reddish-pink hues. “Very unexpectedly,” a team led by geochemist Ann Ollila of Los Alamos National Laboratory wrote in a conference summary, “SuperCam’s TRL analysis of three plagioclase-rich float rocks on the crater rim was found to exhibit clear signatures of chromium-bearing corundum.” Now, the researchers have published their full analysis in Geophysical Research Letters – and made laboratory comparisons that revealed striking similarities between the Martian signal and those from Earth’s precious gems. Corundum was found in three different rocks. (Ollila et al., Geophys. Res. Lett., 2026) This is the first time corundum has been identified in a Martian environment, and the discovery is notable not because the minerals are ones we consider valuable, but because the conditions under which they normally form are not easily explained on Mars. “Its formation generally requires massive aluminum-enriched and silicon-depleted compositions and typically forms at high temperatures or in association with tectonic processes,” Ollila and colleagues write in their paper. “Thus, its detection in Martian rocks is surprising.”Mars does not lack heat, or at least it did not lack it in the past. Its surface is riddled with volcanic features and Jezero Crater contains a large amount of igneous material. No, the problem here lies in chemistry. Corundum is the crystalline form of aluminum oxide and its formation generally requires a lot of aluminum and not a lot of silicon, because if there are silicate minerals around, they will absorb all the aluminum to form aluminum silicate rocks such as plagioclase feldspar. You’ve probably already seen corundum. enigma. The three corundum detections made by Perseverance were made in rock chunks dominated by plagioclase. That’s a mess, especially since the rocks were found in different places along the crater rim. Natural color mosaics of the three rocks. (Ollila et al., Geophys. Res. Lett., 2026) It is not that plagioclase and corundum cannot coexist. The fact is that the conditions for their coexistence are difficult to find on Mars. The three rocks, named Hampden River, Coffee Cove and Smiths Harbor, were pale chunks rich in plagioclase, and all three were what are known as float rocks. These are pieces of rock sitting in the ground that are no longer attached to the bedrock in which they were formed, meaning they may have been transported from somewhere else. Floating rocks are interesting targets for study because they can tell us about the broader geology of Mars without the rover having to travel to a different area. One by one, in March, April, and July 2025, Perseverance examined each rock using time-resolved luminescence (TRL) spectroscopy. It uses a laser to excite atoms within minerals, then measures the characteristic light they emit as they return to their normal state. When Perseverance performed this analysis on the three plagioclase samples, the resulting spectra yielded the distinctive signature of chromium-bearing corundum. So, disappointingly, there were no sparkling rubies scattered across the surface of Mars as if a careless dragon had spilled treasure, but there was spectral evidence of tiny grains of chromium-containing corundum trapped inside. three separate fragments of plagioclase. Still, when the researchers compared those spectra to proportional spectra of ruby, sapphire, and diaspore on Earth, things got interesting. Ruby on Earth gets its brilliant hue from traces of chromium. (StrangerThanKindness/Wikimedia Commons/CC BY-SA 3.0) The three Martian rocks had two prominent luminescence peaks at wavelengths of 692.7 and 694.1 nanometers, the characteristic type of peaks produced in corundum when chromium atoms replace some aluminum atoms, as occurs in ruby. And in Smiths Harbor, the only sample for which it was measured, the brightness remained for about 3 milliseconds, exactly in the range measured for terrestrial corundum. So are there rubies on Mars? Well, maybe. But the more interesting question is: How does Mars produce something that behaves like rubies? And the answer could be right in front of us: Jezero Crater itself. There are several ways corundum could have formed, including through magma or interactions between rocks and hot fluids. But Ollila and his colleagues favor another possibility: the colossal impact that excavated Jezero Crater from the Martian surface billions of years ago. Large impacts subject rocks to tremendous heat and pressure, producing conditions similar to those that create metamorphic minerals deep in the Earth’s crust. Corundum has even been found in rocks altered by impacts on Earth and the Moon. The clues are circumstantial, but convincing. Corundum on Mars occurs in tiny grains; the rocks were found on the edge of the Jezero crater; and were sitting near rocks interpreted as impact breccia: chunks of rock formed in an impact. Researchers even think that fluids interacting with the rocks may have helped create the aluminum-rich, silicon-poor chemistry that would have facilitated the formation of corundum; There is also evidence of past hydrothermal activity at Jezero. Related: Scientists Opened a Mars Meteorite and Found a Big Surprise Other explanations can’t be ruled out, and there’s a lot we can do here from Earth when the minerals are half the Solar System away. Finding the outcrop from which the floating rocks originated would be helpful. Even better would be to return some of it to Earth. That’s a strong argument for reviving the Mars sample return mission that has fallen by the wayside. “If a core sample were obtained from this outcrop and returned to Earth,” they write, “many more analyzes could be performed to conclusively determine how this corundum formed, providing a more complete understanding of Martian history.” The findings have been detailed in Geophysical Research Letters. This article was fact-checked by Rachel Garner and edited by Rebecca Dyer. While we take pride in our process, we are human. If you spot an error, please let us know.
