You got it arse about. As far as I understand, rare earths and...

You got it arse about. As far as I understand, rare earths and other substances (such as industrial diamonds and carbon black) are the output of the flash joule process. The feedstock is any carboniferous waste such as coal, coal dust, fly-ash, rubber (old tyres should suit). And the catalyst for flash joule heating is niobium.

But the most common use of niobium is for producing steel. It appears to be an amazing piece of science where the tiniest drop of niobium will produce an incredibly high strength steel alloy. The steel can increase its strength by simply adding 0.03% - 0.05% niobium. 90% of the world's extracted niobium is currently used to produce this high strength steel.

Niobium is relatively rare, difficult to refine, and highly resistant to chemical attack. It is malleable and hypoallergenic, and also a superconductor. Niobium is currently priced higher than spot silver.

But we all would have been close to niobium as it is also used as the filament in the incandescent lightbulbs in our homes.

https://newatlas.com/materials/carbon-graphene-diamond-flash-joule-heating/