www.sciencealert.com/very-unexpected-nasa-rover-zapped-a-rock-on-mars-and-found-a-gemstone-surprise
When NASA's Perseverance rover used its laser to tease apart some pale rocks lying around in Jezero Crater in 2025, scientists did not expect anything out of the ordinary.
Little did they know what was in store.
The rocks contained something never before found on Mars – a mineral that, here on Earth, can constitute literal treasure.
The mineral was corundum, the crystalline material that forms rubies and sapphires. And there was even a whiff of chromium, which gives rubies their distinctive reddish-pinkish hues.
"Very unexpectedly," wrote a team led by geochemist Ann Ollila of Los Alamos National Laboratory in a conference abstract, "SuperCam's TRL analysis of three plagioclase-rich float rocks in the crater rim were found to exhibit clear signatures of chromium-bearing corundum."
Now, the researchers have published their full analysis in Geophysical Research Letters – and performed laboratory comparisons that revealed striking similarities between the Martian signal and those of precious gems on Earth.
Corundum was found in three separate rocks. (Ollila et al., Geophys. Res. Lett., 2026)
t's the first time corundum has been identified in a Martian setting, and the discovery is remarkable not because the minerals are ones we consider valuable, but because the conditions in which they typically form aren't easily explained on Mars.
"Its formation generally requires bulk compositions enriched in aluminum and depleted in silicon and typically forms at either high temperatures or in association with tectonic processes," Ollila and her colleagues write in their paper.
"Hence, its detection in Martian rocks is surprising."
Mars doesn't lack in the heat department, or at least, it didn't in the past. Its surface is riddled with volcanic features, and Jezero Crater contains a wealth of igneous material.
No, the problem here lies in the chemistry.
Corundum is the crystalline form of aluminum oxide, and its formation usually requires a lot of aluminum and not much silicon – because if there are silicate minerals around, they'll bogart all the aluminum to form aluminum-silicate rocks such as plagioclase feldspar.
You've probably already spotted the corundum conundrum. All three corundum detections made by Perseverance were in chunks of rock dominated by plagioclase. That's one dilly of a pickle – not least because the rocks were found in different locations along the crater rim.
It's not that plagioclase and corundum can't coexist. It's that the conditions for their coexistence are tricky to come by on Mars.
The three rocks – named Hampden River, Coffee Cove, and Smiths Harbour – were pale plagioclase-rich chunks, and all three were what are known as float rocks. Those are chunks of rock sitting on the ground that are no longer attached to the bedrock they formed in, meaning they may have been transported from elsewhere.
Float 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 of 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 subside to their normal state.
When Perseverance performed this analysis on all three of the plagioclase samples, the resulting spectra returned the distinctive signature of chromium-bearing corundum.
So, disappointingly, no sparkling rubies scattered across the surface of Mars like a careless dragon had spilled a hoard – but the spectral evidence for tiny grains of chromium-bearing corundum trapped inside three separate plagioclase chunks.
Still, when the researchers compared those spectra to commensurate spectra from ruby, sapphire, and diaspore on Earth, things got interesting.
Ruby on Earth gets its brilliant hue from trace amounts of chromium (StrangerThanKindness/Wikimedia Commons/CC BY-SA 3.0)
All three Martian rocks had two prominent luminescence peaks at wavelengths of 692.7 and 694.1 nanometers – the characteristic kind of peaks produced in corundum when chromium atoms replace some aluminum atoms, as they do in ruby.
And in Smiths Harbour – the one sample for which this was measured – the glow lingered for about 3 milliseconds, squarely in the range measured for terrestrial corundum.
So are there rubies on Mars? Well, maybe. But the more interesting question is: How does Mars make something that behaves like rubies?
And the answer might be staring us in the face: Jezero Crater itself.
There are several ways the corundum could have formed, including through magma or interactions between rock and hot fluids. But Ollila and her colleagues favor another possibility – the colossal impact that gouged Jezero Crater out of 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 within Earth's crust. Corundum has even been found in impact-altered rocks on Earth and the Moon.
The clues are circumstantial, but compelling.
The corundum on Mars occurs in tiny grains; the rocks were found on the rim of Jezero Crater; and they were sitting close to rocks interpreted as impact breccias – chunks of rock formed in an impact.
The researchers even think fluids interacting with the rocks may have helped create the aluminum-rich, silicon-poor chemistry that would have facilitated corundum's formation; there is evidence for past hydrothermal activity in Jezero, too.
Other explanations cannot be ruled out, and there's only so much we can do here from Earth when the minerals are half a Solar System away.
Finding the outcrop from which the float rocks originated would help. Better still would be getting a piece of it back to Earth.
That's a strong case 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, "vastly more analyses could be conducted to conclusively determine how this corundum formed, which would provide a more complete understanding of Martian history."
The findings have been detailed in Geophysical Research Letters
