Rhodium

Rhodium is the world's most rare non-radioactive metal. The substance is far more expensive than silver and gold, costing over $545 per gram (almost $17,000 per ounce). Rhodium is extremely uncommon, which accounts for its high price. The silvery-white metallic element is very rare, occurring in as little as "one part per 200 million in the Earth's crust," making it extremely difficult to locate and extract.

One of the most common uses for the element is in three-way catalytic converters in vehicles. Rhodium is generally alloyed with platinum or palladium and used in high-temperature and corrosion-resistant coatings due to its inertness to corrosion and most hostile chemicals, as well as its scarcity. To improve its beauty, white gold is frequently plated with a thin rhodium coating, whereas sterling silver is frequently rhodium-plated to prevent tarnishing. Rhodium is occasionally used to cure silicones, which are made up of two parts, one of which contains a silicon hydride and the other of which contains a vinyl-terminated silicone. A rhodium complex is present in one of these liquids.

William Hyde Wollaston discovered rhodium (or Rh) in 1803 when he recovered it from a chunk of platinum from South America. The element is now most commonly utilized in systems that transform toxic engine emissions into less dangerous gases. It's also used to finish jewelry since it's long-lasting and tarnishing-resistant.

Estimated Value: $545 per gram