The most expensive material in the world? It's not diamond, platinum or plutonium. Not even close. It's a material called endohedral fullerenes, which are molecules consisting of spherical cages of carbon atoms that house nitrogen atoms. This microscopic substance is the result of 12 years of work by a company spun out of Oxford University. Its intended use is for atomic clocks. Traditionally, atomic clocks are constructed with cesium atoms, but the Oxford team claims endohedral fullerenes keep time better. These molecules have another advantage. Cesium-based atomic clocks are about the size of a small room, but these clocks can fit on a microchip within mobile phones. Which means the technology could also greatly improve the accuracy of GPS--down from a few feet to one millimeter. Which brings us to why the material is currently worth much, much more than it's weight in gold: the current craze over the nascent self-driving car industry. An industry desperately in need of more accurate navigation systems. At a recent auction, 200 micrograms of pure endohedral fullerenes sold for $33,000. That comes out to about 150 million US dollars per gram! I wonder how long it will be before some celebrity billionaire tries to make jewelry out of this stuff.