A new-to-us mineral

Reto Gieré of the School of Arts and Sciences and colleagues say the new mineral may help immobilize nuclear waste.

 "close up view of the mineral"
Scanning electron microscope image of a hydrokenopyrochlore crystal. (Photo: Philippe Roth, ETH Zürich)

A new mineral has been isolated from a sample of igneous rock in central Madagascar. 

Reto Gieré, a professor and chair of the Department of Earth and Environmental Science in the School of Arts and Sciences, worked with European colleagues to study the sample, which they first learned of through a French mineral dealer who thought it had an unusual appearance. One of Gieré’s colleagues approached him, asking if he’d like to investigate further because the mineral displayed characteristics usually attributed to the pyrochlore mineral group, one of Gieré’s specialties.

“Since I have experience working with this group of minerals, I said I would love to,” says Gieré. “The mineral dealer was right; we saw we had a mineral that was interesting, and perhaps even new.”

The tan and beige material had a resinous luster. Gieré and colleagues analyzed its chemical composition using an electron microprobe, which images the sample like an electron microscope but also allows users to quantitively determine the sample’s chemical composition. They also employed X-ray diffraction to determine its crystal structure. Combined, the analyses confirmed the mineral to be a new species. 

The team named it hydrokenopyrochlore: “hydro” referring to the abundance of water in the mineral’s structure and “keno,” which means empty in Greek, referring to the numerous vacancies, or open spaces, in its crystal structure. 

Identifying new minerals is not entirely uncommon, with new ones found each year, but Gieré says hydrokenopyrochlore is particularly noteworthy because minerals in the pyrochlore group have properties that have been proven valuable. 

“They can be used for nuclear waste immobilization, solid electrolytes, exhaust control in cars, fuel cells, and more,” he says. “This mineral group is of great interest.”

Researchers have developed synthetic pyrochlore phases in the lab and successfully incorporated radioactive materials into their structures.

“This immobilizes the radionuclides into a solid material,” says Gieré. “Pyrochlore is stable for millions of years, so this could eventually provide an excellent container for high-level nuclear waste, including cesium and even plutonium.”