Strange diamonds formed after outer space incident

Strange diamonds from an ancient dwarf planet in our solar system may have formed shortly after the dwarf planet collided with a large asteroid* about 4.5 billion years ago, according to scientists.

The research team confirmed the existence of a rare hexagonal* form of diamond called "lonsdaleite", after analysing ureilite* meteorites* that came from the dwarf planet.

Lonsdaleite is named after the famous British crystallography* pioneer* Dame Kathleen Lonsdale (1903-1971), the first woman elected as a Royal Society Fellow*.

The team found evidence of how lonsdaleite formed by studying ureilite meteorites that had landed on Earth.

RMIT Microscopy* and Microanalysis Facility director Professor Dougal McCulloch, one of the senior researchers involved, said the team predicted the hexagonal structure of lonsdaleite's atoms made it potentially harder than regular diamonds, which have a cubic* structure.

"This study proves categorically that lonsdaleite exists in nature," said Prof McCulloch.

"We have also discovered the largest lonsdaleite crystals known to date that are up to a micron in size – much, much thinner than a human hair."

The team said the unusual structure of lonsdaleite could help inform new manufacturing techniques for ultra-hard materials in mining applications.

Prof McCulloch and his RMIT team – PhD scholar Alan Salek and Dr Matthew Field – used advanced electron microscopy techniques to capture solid and intact slices from the meteorites to create snapshots of how lonsdaleite and regular diamonds formed.

"There's strong evidence that there's a newly discovered formation process for the lonsdaleite and regular diamond, which is like a supercritical* chemical vapour deposition* process that has taken place in these space rocks, probably in the dwarf planet shortly after a catastrophic collision," Prof McCulloch said.

"Chemical vapour deposition is one of the ways that people make diamonds in the lab, essentially by growing them in a specialised chamber."

Published in the Proceedings of the National Academy of Sciences (PNAS) journal, the study was led by Monash University geologist Professor Andy Tomkins.

Prof Tomkins said the team proposed that lonsdaleite in the meteorites formed from a supercritical fluid at high temperature and moderate pressures, almost perfectly preserving the shape and textures of the pre-existing graphite*.

"Later, lonsdaleite was partially replaced by diamond as the environment cooled and the pressure decreased," Prof Tomkins said.

"Nature has thus provided us with a process to try and replicate in industry. 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."

Prof Tomkins said the study findings helped address a longstanding mystery regarding the formation of carbon phases in ureilites.

CSIRO's Dr Nick Wilson said the collaboration of technology and expertise from different institutions allowed the team to confirm the lonsdaleite with confidence, with scientists from Monash University, RMIT University, CSIRO, the Australian Synchrotron and Plymouth University taking part.

An electron probe micro-analyser* was used at CSIRO to quickly map the relative distribution of graphite, diamond and lonsdaleite in the samples.

"Individually, each of these techniques give us a good idea of what this material is, but taken together – that's really the gold standard," Dr Wilson said.

GLOSSARY

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CLASSROOM ACTIVITIES1. Production of lonsdaleiteAfter reading the Kids News article about lonsdaleite and how it is formed, create a circular flow chart showing the full production process. Try and keep the flow-chart simple by using only key words for each stage of the process.

Time: allow 20 minutes to complete this activityCurriculum Links: English; Science; Critical and Creative Thinking

2. Extension If you could design a piece of jewellery using one or more of these lonsdaleite diamonds, what would it be?

Sketch your design below.

Time: allow 15 minutes to complete this activityCurriculum Links: English; Visual Arts

VCOP ACTIVITY I spy nounsNouns are places, names (of people and objects), and time (months or days of the week).

How many nouns can you find in the article?

Can you sort them into places, names and time?

Pick three nouns and add an adjective (describing word) to the nouns.