The mysterious mineral

Humans love a mystery. Just look at our collective fascination with the Loch Ness Monster, Jack the Ripper, Donald Trump’s hair, Adam Sandler’s movie career, and the continued culinary success of the sausage. When things are without explanation they take on a grandeur and significance that tickles our primal desire to “know”. As a species we pride ourselves on the ability to analyse and understand…we get off on the complexity of things. We have come from the simplicity of experiencing the world, are in a phase where we need to understand everything, and hopefully will one day return to simple experience of things again but this time with awareness. For now though, understanding things in a complex way gets our rocks off and when something eludes analysis, like a dog with a lizard caught under a bush, we just have to go back to it. One such mysterious lizard for the scientific community has been an elusive mineral. This might not sound too jazzy until you realise that the mineral in question is actually the most abundant mineral on the planet and it has been unable to be captured…until now, and, in typical Homo sapiens sapiens style (yes, that is a correct and deliberate duplication there), having captured it we also named it.

For many years now scientists have believed in the existence of a mineral that makes up about 38 per cent of the Earth’s total volume. The word “believed” is appropriate because although all tests indicated that this substance is there, it could not be analysed because it does not survive the trip to the surface of the Earth. When brought to the surface it transforms to less dense minerals and it only remains stable at depths below 660 kilometres from the surface and at pressures above 230 kilobars. The nature of this mystery mineral is relevant to our understanding of the Earth because its properties influence how other elements and heat flow through the planet’s mantle. Now researchers have managed to get hold of some this mineral but not from within the Earth.

When asteroids collide out there in deep space, the shock of the collisions create the same conditions of deep Earth, around 2,100 degrees Celsius and pressures around 240,000 times greater than the air pressure at sea level. The shock impact occurs rapidly enough that the mineral we are looking for is captured and does not break down when exposed to lower pressure, as happens when we try to bring it up from within the Earth. That might sound all very well but how can asteroid collisions help us?

Space debris is flying around the Universe constantly and then galactic shrapnel from these asteroid collisions occasionally falls to Earth as meteorites and those meteorites have the mystery mineral locked within shock-melted veins that withstand the low pressure of the Earth’s surface. Unfortunately previous attempts to extract the mineral from meteorites using transmission electron microscopy have caused radiation damage to the mineral.

In an exciting move researchers have now used non-damaging micro-focused x-rays for diffraction analysis of the mineral. They used a sample from the Tenham meteorite which crashed into Australia in 1879. The result was that they found the mineral is a high density form of magnesium iron silicate that is higher in both iron and sodium than was expected.

Now we have analysed it of course, we have to name it. The name decided upon for this, our planets most abundant mineral is “Bridgmanite”, after Percy Bridgman who won the 1964 Nobel prize for his pioneering work in high-pressure research. It is a nice acknowledgment although in the opinion of this column, “Percy” would have been a better choice.