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.
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.
The report appeared in the journal Nature Communications.
