From Seagull Poop to Plutonium: The Most Valuable Substances in the World By John Csiszar of GOBankingRates | Rare and beautiful items have always had a grip on the imagination — and finances — of humankind. Since ancient times, precious minerals like gold have been revered and used in everything from jewelry and dinnerware to the sacred tombs of emperors. More recently, gold is even used to bring opulence to modern electronics such as iPhones. To a large degree, “value” is assigned to an object based on the long-standing economic principle of supply and demand. Typically, as demand increases and supply decreases, the price of an item rises, and vice versa.