Francium - If you want to buy a Gram of francium, you need to pay at least a billion dollars. Although, even if you had that kind of cash laying around, you probably wouldn't be able to get your hands on this material. In fact, one gram of francium has never been observed. Because the half-life of this element is about 22 minutes, which means any viewable quantity of the element would immediately vaporize. But it is assumed that francium would appear as a highly reactive metal. The largest amount of this element that has ever been produced in the laboratory was a cluster of more than 300,000 atoms. Realistically, nobody would be willing to pay billions of dollars for something that will disappear within minutes ans has no practical use whatsoever.

Californium - Californium is radioactive element that doesn't occur naturally on earth. The estimated cost of one gram of californium is about $27 million, which make perfect sense considering the fact that the global production of californium is a half gram per year. To create it you need either a particle accelerator or nuclear reactor. The element is almost insoluble in water, but it adheres well to ordinary soil. Only one microgram of californium is needed to release 170 million neutron particles every minute. It is used as a neutron source to identify silver and gold ores. It is also used in neutron moisture guage, which helps to find water and oil bearing layers in oil wells.

Carbon - Carbon is one of the most essential elements for life. Although a large amount of it is present in all of our bodies, and things like coal and graphite aren't expensive as we all know. But if carbon atoms arranged in certain order it can have an extremely high value. In the form of diamond, carbon can cost you as much as $65,000 for one gram.

Plutonium - If you know anything about plutonium, it shouldn't come as a surprise that it's of the most expensive substances on the planet. Sitting at cost of $4,000 per gram. Its scarcity is a major reason for its high price. However, its value is derived more from its usefulness in nuclear applications. In fact, there are only two uses for plutonium. The relatively benign option is to use plutonium to fuel nuclear reactors. The scarier application is for nuclear weapons.

Scandium - Scandium is another rare earth metal that has high price due to rarity. Because of its usefulness in aluminum alloys, scandium is one of the most highly traded metals on earth. One gram of scandium will cost you at least $270. 10 tonnes of scandium are traded per year, that quickly adds up to $2.7 billion annually. With prices like this, be glad that the jewelry you buy is made out of something as affordable as gold!