Asteroid impacts on Earth make structurally bizarre diamonds, say ASU scientists

November 20, 2014

Scientists have argued for half a century about the existence of a form of diamond called lonsdaleite, which is associated with impacts by meteorites and asteroids. A group of scientists based mostly at Arizona State University now show that what has been called lonsdaleite is in fact a structurally disordered form of ordinary diamond.

The scientists' report is published in Nature Communications, Nov. 20, by Péter Németh, a former ASU visiting researcher (now with the Research Centre of Natural Sciences of the Hungarian Academy of Sciences), together with ASU's Laurence Garvie, Toshihiro Aoki and Peter Buseck, plus Natalia Dubrovinskaia and Leonid Dubrovinsky from the University of Bayreuth in Germany. Buseck and Garvie are with ASU's School of Earth and Space Exploration, while Aoki is with ASU's LeRoy Eyring Center for Solid State Science. extreme close-up of diamond grains from Canyon Diablo meteorite Download Full Image

"So-called lonsdaleite is actually the long-familiar cubic form of diamond, but it's full of defects," says Péter Németh. These can occur, he explains, due to shock metamorphism, plastic deformation or unequilibrated crystal growth.

The lonsdaleite story began almost 50 years ago. Scientists reported that a large meteorite, called Canyon Diablo after the crater it formed on impact in northern Arizona, contained a new form of diamond with a hexagonal structure. They described it as an impact-related mineral and called it lonsdaleite, after Dame Kathleen Lonsdale, a famous crystallographer.

Since then, "lonsdaleite" has been widely used by scientists as an indicator of ancient asteroidal impacts on Earth, including those linked to mass extinctions. In addition, it has been thought to have mechanical properties superior to ordinary diamond, giving it high potential industrial significance. All this focused much interest on the mineral, although pure crystals of it, even tiny ones, have never been found or synthesized. That posed a long-standing puzzle.

The ASU scientists approached the question by re-examining Canyon Diablo diamonds and investigating laboratory samples prepared under conditions in which lonsdaleite has been reported.

Using the advanced electron microscopes in ASU's Center for Solid State Science, the team discovered, both in the Canyon Diablo and the synthetic samples, new types of diamond twins and nanometer-scale structural complexity. These give rise to features attributed to lonsdaleite.

"Most crystals have regular repeating structures, much like the bricks in a well-built wall," says Peter Buseck. However, interruptions can occur in the regularity, and these are called defects. "Defects are intermixed with the normal diamond structure, just as if the wall had an occasional half-brick or longer brick or row of bricks that's slightly displaced to one side or another."

The outcome of the new work is that so-called lonsdaleite is the same as the regular cubic form of diamond, but it has been subjected to shock or pressure that caused defects within the crystal structure.

One consequence of the new work is that many scientific studies based on the presumption that lonsdaleite is a separate type of diamond need to be re-examined. The study implies that both shock and static compression can produce an intensely defective diamond structure.

The new discovery also suggests that the observed structural complexity of the Canyon Diablo diamond results in interesting mechanical properties. It could be a candidate for a product with exceptional hardness.

The School of Earth and Space Exploration is an academic unit of ASU's College of Liberal Arts and Sciences.

Robert Burnham

Science writer, School of Earth and Space Exploration


Researchers explore future of 'postdigital' textbook

November 20, 2014

An interdisciplinary team at Arizona State University has been awarded a grant from the National Science Foundation’s Cyberlearning and Future Learning Technologies program to conduct research on the future of the textbook.

The project focuses on the “postdigital textbook,” a new type of educational technology that combines personalized learning with community-driven features that encourage collaboration and resource sharing, and emphasize learning as a social process. An image of a floating book made of glowing binary code Download Full Image

"Digital textbooks are here, but they’re boring,” says Ruth Wylie, assistant director of the Center for Science and the Imagination and assistant research professor in the Mary Lou Fulton Teachers College. “This project is an opportunity to experiment with new models for what a textbook can be that will motivate and even inspire students and teachers.”

The principal investigator on the project, titled “Towards Knowledge Curation and Community Building within a Postdigital Textbook,” is Erin Walker, an assistant professor in the School of Computing, Informatics and Decision Systems Engineering, one of ASU’s Ira A. Fulton Schools of Engineering. The co-investigators are Wylie and Ed Finn, director of the Center for Science and the Imagination and assistant professor in the School of Arts, Media and Engineering and the Department of English.

The project is funded as an Early-concept Grants for Exploratory Research (EAGER) grant, which supports exploratory work in its early stages on previously untested but potentially transformative high-impact research ideas.

“The postdigital textbook goes beyond just digitizing print books or replacing still images with videos,” says Wylie. “Instead, it is a tool that helps students curate knowledge and build community with their classmates."

The project is part of an ongoing collaboration among Walker, Wylie and Finn that will eventually lead to the development of working prototypes of postdigital textbooks that can be tested in classroom environments.

The initial phase of the project involves surveying existing research and working with teachers and students to determine what particular behaviors, relationships and goals the postdigital textbook should facilitate to optimize learning.

“The traditional paper textbook is a technology that has been honed and refined over decades,” says Walker. “It offers numerous helpful affordances, or student and teacher behaviors that the technology enables and encourages, like taking notes in the margins, highlighting words and phrases, using the index and table of contents to look up key concepts, and so forth.

“The challenge here is to develop a digital textbook that provides new, intuitive affordances without taking away any of the useful and time-tested features that we all take for granted when we use a physical book,” she says.

Digital technology enables learning materials in digital textbooks to be precisely tailored to students’ needs, interests and learning styles. The postdigital textbook embraces personalization but recognizes that textbooks are effective precisely because they are stable, shared resources that all students can refer to and discuss equally.

“This project is about determining how we need to design textbooks of the future so that they adjust to the strengths and limitations of individuals while also helping students build 21st century skills like working collaboratively in groups and curating and presenting multimedia resources," says Finn.

Joey Eschrich

program manager, Center for Science and the Imagination