Platinum Platinum, symbol Pt, is a relatively rare, chemically inert metallic element that is more expensive than gold. The atomic number of platinum is 78. Platinum is one of the transition elements in group 10 of the periodic table. Platinum is the most important of the group of elements called the platinum metals, also included in this group is the metals: ruthenium, rhodium, palladium, osmium, and iridium. Platinum metals were probably used in alloyed forms in ancient Greece and Rome and were first mentioned in European literature in the early 16th century. The separation of the other platinum metals from platinum and from each other was accomplished in the e