Ask what the most abundant mineral on Earth is and the reasonable answer is feldspar, which makes up around 60 percent of the crust, as set out in feldspar. But the crust is a rounding error. It is under one percent of the planet by volume.
Count the whole Earth and the answer changes completely. Roughly 38 percent of the planet by volume is a single mineral, and it did not receive an official name until 2014.
Why it took so long
Bridgmanite is a magnesium iron silicate with a perovskite structure that makes up the bulk of the lower mantle, from about 660 kilometres down to the core-mantle boundary near 2,900 kilometres. Its existence and properties had been inferred for decades from seismology and from laboratory experiments in diamond anvil cells.
The problem was the naming rules. As described in how a new mineral becomes a mineral, the international commission requires a natural sample, structural and chemical data from that sample, and a type specimen deposited in a museum. Synthetic material and theoretical models do not qualify, no matter how good the evidence.
And bridgmanite cannot survive the trip up. Its structure is only stable under lower-mantle pressures. Decompress it and it reverts to other minerals long before it reaches the surface. Every sample brought up by any geological process has already transformed.
The shocked meteorite that solved it
The answer came from space. The Tenham meteorite, which fell in Australia in 1879, contains tiny grains formed during a high-energy collision between asteroids in space. The shock pressures in that collision briefly reached lower-mantle conditions, and the resulting high-pressure phases were then quenched fast enough to survive.
In 2014, researchers characterised natural bridgmanite grains in Tenham using synchrotron X-ray diffraction on crystals just a few micrometres across, and the mineral was finally approved and named for Percy Bridgman, the physicist who won a Nobel Prize for high-pressure research.
So the most abundant mineral on the planet was formally described from a meteorite, using the same shock-metamorphic principles as shocked quartz. Everything about that is worth sitting with.
The rest of the hidden inventory
Bridgmanite is not alone. Ferropericlase makes up much of the remaining lower mantle. Below about 2,700 kilometres, bridgmanite converts to post-perovskite, a phase only discovered in 2004 and thought to explain a long-puzzling seismic layer just above the core.
Ringwoodite, a high-pressure form of olivine, occurs in the transition zone around 520 to 660 kilometres. In 2014 a ringwoodite inclusion inside a diamond from Brazil was found to contain around one percent water by weight, delivered to the surface by the mechanism described in kimberlite pipes. If the transition zone is broadly similar, it may hold as much water as all the oceans combined, locked into crystal structures rather than existing as liquid.
What it changes about the word mineral
We tend to picture minerals as things you can hold. On a planetary scale, almost none of them are. The overwhelming majority of Earth’s mineral matter exists at pressures and temperatures where no human will ever sample it directly, and our entire collecting tradition works from the thinnest possible skin of the planet.
Which puts a quartz point in perspective. A clear quartz point is not typical Earth material. It is a rarity from an unusual, cool, low-pressure surface layer, and the fact that it is stable enough to sit on a shelf is itself a geological accident.
