Usually, what springs to mind when you think of the world's most expensive substances are gold, silver, and platinum. However, according to a study conducted by the BBC's ‘Science Focus,' the reality is much different, and they are not what you would expect them to be… Helium Valued at approximately $3 million per gram, Helium-3, a lighter form of the original helium, is a descendant of the rare hydrogen variant tritium, which produces only 22-44 lbs of the substance annually.  Emerald Valued at $483 million per gram, these gemstones are derived from the beryl mineral, with its renowned shade of green stemming from the elements chromium and vanadium. Emerald gemstones are quite rare and hold cultural significance due to their ties with royalty, emblematic of high status.  Red Diamonds These rare and lucrative diamonds are valued at approximately $4.7 million per gram and can only be found in three diamond mines: Brazil, South Africa, and Western Australia. Scientists believe that these red diamonds are so rare due to the way the light reacts with the diamond; fewer than 30 of this diamond variation can be found in the world.  Asteroid Bennu Samples Gathered by the University of Arizona on NASA's ‘OSIRIS-REx' mission to study its composition, this sample from the near earth asteroid Bennu is valued at $9.6 million per gram. Californium This radioactive substance, strictly made in nuclear reactors or particle accelerators, is valued at $25.6 million per gram due to its high volume of neutrons. Nitrogen atom-based endohedral fullerenes This man-made metamaterial is mostly used in creating strong, lightweight materials in aerospace engineering and electronics.  These minuscule cylindrical structures, which are valued at approximately $134 million per gram, could be used as atomic clocks, crucial in satellite navigation.  Antimatter Artificially manufactured in special particle accelerators in underground locations along the French-Swiss border, antimatter is valued at $59.8 trillion, with annual running costs of $977,000. Although this substance remains unharnessed, it has the potential to solve the Earth's power needs and could even make interstellar travel a reality.