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A newly discovered solid form of boron has a remarkable structure: 20-sided cages made of boron atoms interspersed with smaller groups made of two boron atoms. These cages and groups alternate in a 3-D lattice, much like the arrangement of large chloride ions and small sodium ions in table salt. It’s the first stable form of boron to be experimentally confirmed, and the first ionic, saltlike solid scientists have found that’s made from a single element.

“Finding an ionic structure of an element is something stunning,” says Artem Oganov, a theoretical crystallographer at Stony Brook University in New York and coauthor of the study, which appears in the Jan. 29 Nature.

Boron is a squirrelly element, sometimes behaving like a metal and other times like an insulator. Because of boron’s odd chemical behavior, the natural, stable forms that the element assumes at various temperatures and pressures — analogous to the icy, vaporous and liquid forms of water — have been difficult to confirm. Aside from the transition elements at the bottom of the periodic table, boron is “the only element whose phase diagram is unknown from experiment,” Oganov says. — Patrick Barry

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