|This image shows a fragment of the 4.5 billion-year-old Tenham meteorite that contains tiny crystals of bridgmanite. Image credit: Chi Ma.|
High-pressure and temperature experiments strongly suggest that (Mg,Fe)SiO3-perovskite, a silicate mineral with a perovskite structure, is the dominant material in the lower mantle of Earth.
Although synthetic examples of this mineral have been well studied, no naturally occurring samples had ever been found in a rock on the planet’s surface.
Thanks to the work of mineralogists Dr Chi Ma from California Institute of Technology and Prof Oliver Tschauner from the University of Nevada-Las Vegas, naturally occurring (Mg,Fe)SiO3-perovskite has been found in the Tenham meteorite – a fragment of a larger, 4.5 billion-year-old meteorite that fell in Queensland, Australia, in 1879.
Because the Tenham meteorite had survived high-energy collisions with asteroids in space, parts of it were believed to have experienced the high-pressure conditions found in the Earth’s mantle. That, scientists thought, made it a good candidate for containing (Mg,Fe)SiO3-perovskite, now simply called bridgmanite.
The scientists used synchrotron X-ray diffraction mapping to find indications of the bridgmanite. They then examined the mineral and its surroundings with a high-resolution scanning electron microscope and determined the composition of the tiny bridgmanite crystals using an electron microprobe.
In March 2014, the team submitted a proposal to the International Mineralogical Association Commission on New Minerals, Nomenclature and Classification (CNMNC) with the suggested name of bridgmanite. CNMNC approved the mineral and its name.
“It is a really cool discovery. Our finding of natural bridgmanite not only provides new information on shock conditions and impact processes on small bodies in the solar system, but the tiny bridgmanite found in a meteorite could also help investigations of phase transformation mechanisms in the deep Earth,” Dr Ma said.
The study was published in the journal Science.