Scientists solve meteorite mystery with high-pressure X-ray experiments

"Our study clarifies how squeezed cristobalite can transform into seifertite at much lower pressure than expected," said researcher Ana Černok
By Brooks Hays  |  June 7, 2017 at 11:18 AM
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June 7 (UPI) -- Scientists have long struggled to understand how different types of silica, which require distinction formation conditions, are commonly found in the same meteorite.

Thanks to PETRA III, the X-ray light accelerator at DESY, the German research facilities, scientists finally have some answers.

Researchers used high-pressure experiments to better understand the conditions under which different types of quartz minerals form.

The mineral silicon dioxide, or cristobalite, is rare on Earth, but is common in meteorites sourced from the moon and Mars. It is only formed under unique, high-temperature conditions.

In many moon and Mars meteorite fragments found on Earth, scientists have discovered cristobalite coexisting with seifertite, another form of silica. Seifertite only forms under extremely high pressures.

"Finding cristobalite and seifertite in the same grain of meteorite material is enigmatic, as they form under vastly different pressures and temperatures," Leonid Dubrovinsky, a planetary scientist at the University of Bayreuth, said in a news release. "Triggered by this curious observation, the behavior of cristobalite at high-pressures has been examined by numerous experimental and theoretical studies for more than two decades, but the puzzle could not be solved."

X-ray accelerators at DESY allowed researchers to observe the behavior of cristobalite under extreme pressure with unprecedented clarity. The images suggest the mineral adopts a new phase while subjected to high pressures, but reverts to its normal form once the pressure is released.

However, if extreme pressures are exerted unevenly, researchers found cristobalite can be transformed into seifertite. The experiments also showed the conversion of cristobalite to seifertite can occur at much lower pressures than is required for the transformation of basic silica into seifertite.

"Our study clarifies how squeezed cristobalite can transform into seifertite at much lower pressure than expected," said researcher Ana Černok, who know works at Open University. "Therefore, meteorites that contain seifertite associated with cristobalite have not necessarily experienced massive impacts."

The findings -- detailed in the journal Nature Communications -- suggest scientist must reconsider their analysis of meteorites and their assumptions about the types of impacts that yielded them.

"They provide clear evidence that neither cristobalite nor seifertite should be considered as reliable tracers of the peak shock conditions experienced by meteorites," Dubrovinsky said.

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