Isotopes in zeolites defy nature, opening up new possibilities for carbon capture and storage.

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Zeolites could be considered as nature’s workhorse.

Filled with microscopic holes and channels, these ultraporous minerals can soak up environmental contaminants, filter drinking water, manage nuclear waste, and even absorb carbon dioxide (CO2).

Now, in the first study of its kind, researchers have analyzed ancient zeolite specimens collected from the edges of East Iceland to discover that zeolites separate calcium isotopes in a wholly unexpected way.

“Calcium occurs as multiple isotopes having different masses,” said Claire Nelson, the paper’s first author. “Most minerals preferentially incorporate lighter calcium isotopes. What we found is that some zeolites prefer lighter isotopes to an extreme degree, while other zeolites prefer heavier isotopes, a rare and striking result.”

This finding could help quantify temperatures in both modern and ancient geologic systems, as well as inform efforts to mitigate human-caused climate change by carbon capture sequestration.

The study was published on October 1, 2021, in the journal Communications Earth and Environment, a new open access journal established by Nature Portfolio.

“We discovered something completely unexpected and new,” said Andrew Jacobson, senior author of the study. “It could have wide ranging implications in the geosciences and across fields, especially considering that zeolites have countless applications in industry, medicine and environmental remediation.”

Jacobson is a professor of Earth and planetary sciences at Northwestern’s Weinberg College of Arts and Sciences. Nelson recently earned her Ph.D. working in Jacobson’s laboratory and is currently a postdoctoral research scientist at ’s Lamont-Doherty Earth Observatory. Zeolite expert Tobias Weisenberger, a geologist at the University of Iceland’s Breiðdasvík Research Center, was a key co-author of the study.

Although they form in a wide variety of geologic environments, zeolites are particularly common in volcanic settings that produce basalt. As lava erupted from volcanoes piles up over time, the buried rocks compress and transform. Groundwater interacts with these rocks to form zeolites, which comprise aluminum, oxygen and silicon atoms linked together to make three-dimensional cage-like structures.

“The initial volcanic lava crystallized into primary minerals,” Nelson said. “Then water rained down and infiltrated the rocks, dissolved them and produced secondary minerals like zeolites and calcite.”

To collect samples for the study, Nelson visited the Berufjörður-Breiðdalur region in eastern Iceland, where glacial erosion has carved deep valleys and fjords into basalt rock to reveal buried zeolites. Nelson climbed to the top of the fjord’s mountains and rappelled into the river canyon to collect samples from various altitudes, representing different depths of burial and thus temperatures of metamorphism.

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