With high-pressure experiments at DESY’s X-ray light source PETRA III and other facilities, a research team around Leonid Dubrovinsky from the University of Bayreuth has solved a long-standing riddle in the analysis of meteorites from Moon and Mars. The study, published in the journal Nature Communications, can explain why different versions of silica can coexist in meteorites, although they normally require vastly different conditions to form.
The scientists investigated a silicon dioxide (SiO2) mineral that is called cristobalite. Different from ubiquitous quartz, cristobalite is relatively rare on Earth’s surface, as it only forms at very high temperatures under special conditions. Surprisingly, researchers have also found the silica mineral seifertite together with cristobalite in Martian and lunar meteorites. Seifertite was first synthesized by Dubrovinsky and colleagues 20 years ago and needs extremely high pressures to form. Using the intense X-rays from PETRA III at DESY and the European Synchrotron Radiation Facility ESRF in Grenoble (France), the scientists could now get unprecedented views at the structure of cristobalite under high pressures of up to 83 giga-pascals (GPa), which corresponds to roughly 820,000 times the atmospheric pressure.
But if cristobalite is compressed unevenly under what scientists call non-hydrostatic conditions, it unexpectedly converts into a seifertite-like structure, as the experiments have now shown. This structure forms under significantly less pressure than necessary to form seifertite from ordinary silica.