Iridium, ih RIHD ee uhm, is a silvery metallic element. It is one of the hardest metals, and it resists corrosion better than any other metal. Iridium is rare. It occurs in gravel deposits containing platinum ores. It also occurs in alloys (metal mixtures) with osmium. Most iridium comes from Brazil, Canada, Myanmar, Russia, South Africa, and the United States. Iridium is too brittle to use by itself. Its main use is to increase platinum's strength and resistance to corrosion. Manufacturers use platinum-iridium alloys in containers, machine parts, and electric contacts that are to be exposed to corrosive chemicals and high temperatures. Jewelry and spark-plug electrodes are also made from iridium alloys.