A team of geologists from the University of Alberta, Northwestern University and the University of Glasgow has found a previously unknown mineral in a diamond that formed at great depth.
Broken and rounded dodecahedral diamond from the Koffiefontein kimberlite pipe that hosted goldschmidtite; the mineral is seen in green and radiation damage of the diamond can be seen in the brown regions. Image credit: Meyer et al, doi: 10.2138/am-2019-6937.
A single 100 μm grain of goldschmidtite was found as an inclusion in a dodecahedral diamond from the Koffiefontein kimberlite pipe, Kaapvaal craton, South Africa.
The mineral is dark green with an adamantine luster, and has a density of 5.32 g/cm3.
It has the formula (K,REE,Sr)(Nb,Cr)O3, and is the natural analog of the well-known ferroelectric material KNbO3.
“Goldschmidtite has high concentrations of niobium, potassium, and the rare earth elements lanthanum and cerium, whereas the rest of the mantle is dominated by other elements, such as magnesium and iron,” said Nicole Meyer, a PhD student at the University of Alberta.
“For potassium and niobium to constitute a major proportion of this mineral, it must have formed under exceptional processes that concentrated these unusual elements.”
Goldschmidtite is thought to have formed at a depth of about 106 miles (170 km) below the surface.
“Goldschmidtite is highly unusual for an inclusion captured by diamond and gives us a snap-shot of fluid-processes that affect the deep roots of continents during diamond formation,” said University of Alberta’s Professor Graham Pearson.
The name goldschmidtite is in honor of Victor Moritz Goldschmidt, the founder of modern geochemistry.
“There have been several attempts to name new minerals after Goldschmidt, but previous ones have been discredited. This one is here to stay,” Professor Pearson said.
The discovery is described in a paper in the journal American Mineralogist.
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Nicole A. Meyer et al. 2019. Goldschmidtite, (K,REE,Sr)(Nb,Cr)O3: A new perovskite supergroup mineral found in diamond from Koffiefontein, South Africa. American Mineralogist 104 (9): 1345-1350; doi: 10.2138/am-2019-6937
Source link: https://www.sci.news/geology/goldschmidtite-mineral-earths-mantle-diamond-07624.html
