A Martian meteorite has revealed something unusual: a previously unknown rock type containing garnet, the first time this mineral has been identified on Mars.
This discovery is more than just a mineral discovery. It’s a geological time capsule that holds clues about the extreme temperatures, crushing pressures and hidden processes that shaped the Red Planet billions of years ago.
An international team, including researchers from the University of Portsmouth, hopes that this agate-bearing rock will help piece together the story of Mars dating back 4.5 billion years.
On Earth, garnet is more than just a gemstone admired by the ancient Egyptians, Romans, and Victorian elites, or the January birthstone. In geology, the mineral is a keystone, recording tectonic disturbances, ore formation, and the dancing of fluids and rocks deep within our planet. Now, Mars has joined the opal club, offering scientists a new lens into its fiery past.
Scientists have identified the likely habitat of Martian meteorites
Scientists studying the martian meteorite Northwest Africa (NWA) 8171 have discovered a rock type that contains garnet, a mineral never before seen in samples from Mars.
This represents the first discovery of garnet-bearing stones on the Red Planet, providing researchers with a geological time capsule. Inside are clues about the extreme temperatures, crushing pressures, and hidden processes that shaped Mars billions of years ago.
James Darling, Professor of Earth and Planetary Sciences from the University of Portsmouth’s School of Environment and Life Sciences, said: “The results add a fascinating new dimension to our understanding of the geology of Mars and open an exciting new window on the evolution of our planetary neighbour.”
Meteorite NWA 8171 is part of a rare group of 18 pieces of Martian regolith. These are all fragments of the same old fall. The researchers used precision instruments, including microelectron probes and scanning electron microscopes, to map their minerals, trace chemical signatures, and capture scattered electron images.
Within this cosmic puzzle piece, they identified a piece of agate, the first of its kind from Mars. The clast is divided into two distinct parts: andradite, which contains a diopside domain rich in calcium garnet and pyroxene; and K-feldspar, which contains a large domain comprising a mixture of feldspar and pyroxene.
Tanya Kiesowski, assistant professor of geosciences from Brock University in Canada, said: “This little fragment of the meteorite looked really interesting, and its chemistry was a little strange. At first, we assumed it was a mineral called pyroxene, which is a very common mineral, but then we decided to take a second look.”
Professor Kiesowski said, “Agate is a classic example of a mineral found often in metamorphic rocks on Earth. The metamorphic process transforms igneous or sedimentary rocks into new forms through exposure to intense heat, high pressure, or hot fluids.”
“On Mars, the heat and pressure needed to produce garnet through metamorphism could be the result of a meteorite hitting the Martian surface, magma rising into the Martian crust, or both.”
Similar mineral mixtures are known on Earth in metamorphic environments as skarns, in alkaline igneous rocks, and even as secondary phases in carbonaceous chondrites.
Mineralogical and compositional analyzes indicate that the layer has a complex history, indicating multiple crystallization stages or subsequent alteration events. But because NWA 8171 is a regolith, a mixture of surface debris, the team also wondered: Could this garnet shard come from beyond Mars?
Fossils found in the feldspar-rich area are consistent with Martian values. However, the diopsides in the andradite-bearing zone show more variability. This difference, along with similarities to Earth and chondrite rocks, suggests that garnet may not be a primary igneous mineral. Alternatively, it could have formed during an oxidative metasomatic event on Mars. However, an extra-Martian origin is possible.
The next step is crucial: Researchers will study the isotopic signatures of the garnet to determine whether it actually crystallized on Mars or was delivered from another planetary body.
Kizowski said “Measuring oxygen isotopes from the garnet-bearing rock type itself would help confirm whether it is of Martian origin or from an exotic meteorite. An isotope is a group of atoms with equal numbers of protons and electrons, but different numbers of neutrons.”
The discovery of garnet in the Martian meteorite NWA 8171 is an important discovery with wide-ranging implications. It could indicate a previously unknown magma source on Mars. It may represent the process of minerals changing under different conditions. It could also be a component of regolith resulting from cosmic collisions. Alternatively, it may indicate a metamorphic event deep within the Martian crust.
Magazine reference:
- T.V. Kiesovsky, L.F. White, A. Cernok, Katit et al. Expanding the rock diversity of Mars: discovery of a garnet-bearing layer at NWA 8171. Geochemical Perspectives Letters. Digital ID: 10.7185/geochemistry.2619
