Mysterious folded diamonds traced back to ancient dwarf planet cataclysm
Australian scientists have discovered strangely folded diamonds in rare meteorite samples. In investigating how they came to form, the team found evidence that they were forged in a cataclysm on an ancient dwarf planet.
Diamond is famously the hardest known natural material, and as such it isn’t exactly known for its flexibility. That’s why scientists on the new study were surprised to find diamonds with distinctive folded structures inside meteorites.
Specifically, the meteorites belonged to a class known as ureilites, which are rare, stony, carbon-rich and often contain tiny diamonds. First, researchers at the CSIRO mapped out the distribution of carbon in the samples and what form it took, including diamond and graphite. In doing so, they found evidence that the folded diamond was actually an uncommon hexagonal form known as lonsdaleite.
To confirm, the samples were then passed to a team at RMIT, who examined them using high-resolution transmission electron microscopy (TEM). This not only revealed that the meteorites did contain lonsdaleite, but that they were the largest crystals of the mineral ever found, up to 1 micrometer long. The folded diamonds in the rock, it turned out, were made up of many tiny crystals of lonsdaleite.
But that still didn’t explain how they came to be folded. Further clues came when the team noticed that some of the lonsdaleite had been converted to graphite and cubic diamond, and the team went on to compare the distribution of diamond, graphite and lonsdaleite in 18 different samples of ureilite. From this, they were able to piece together the most likely story.
When they first folded the crystals weren’t actually diamond yet – they were still in the form of the much softer graphite. These would have grown in the mantle of a dwarf planet or large asteroid some 4.5 billion years ago, when the solar system was still forming. Over time, high temperatures and pressure from surrounding material would have warped the graphite into the folded shape seen today.
Later, the parent body must have collided with another massive object in a cataclysm that may have destroyed most of the original planetoid. Not only did this send material scattering to eventually land on Earth as meteorites, but it formed a supercritical fluid that converted the graphite into lonsdaleite. The end result was lonsdaleite that preserved the original shape of the graphite so well that it took on the seemingly impossible appearance of being folded.
The team says that this is more than just a cool story – it could have important applications in manufacturing. This natural process is quite similar to the chemical vapor deposition technique currently used to make industrial diamond tools and parts, and it could provide inspiration for making these things out of lonsdaleite. After all, this hexagonal structure is thought to be more than 50 percent harder than common cubic diamond.
“Nature has thus provided us with a process to try and replicate in industry,” said professor Andy Tomkins, lead author of the study. “We think that lonsdaleite could be used to make tiny, ultra-hard machine parts if we can develop an industrial process that promotes replacement of pre-shaped graphite parts by lonsdaleite.”
The research was published in the journal PNAS.