NEW YORK (TIP): Scientists have long argued about the existence of a form of diamond called lonsdaleite associated with impacts by meteorites and asteroids. A team of scientists largely from Arizona State University (ASU) now show that what has been called lonsdaleite is in fact a structurally disordered form of ordinary diamond. “So-called lonsdaleite is actually the long-familiar cubic form of diamond but it is full of defects. These can occur due to shock metamorphism, plastic deformation or unequilibrated crystal growth,” explained Piter Nemeth, a former ASU visiting researcher.

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. The scientists re-examined Canyon Diablo diamonds. Using the advanced electron microscopes, the team discovered, both in the Canyon Diablo and the synthetic samples, new types of diamond twins and nanometer-scale structural complexity.