Gadolinium

Gadolinium is a silvery rare-earth metal named after the mineral gadolinite, which honors the Finnish chemist Johan Gadolin. Jean Charles Galissard de Marignac detected it in 1880. Like its neighbors, it is mined from rare-earth minerals, mostly in China.

Gadolinium has two unusual talents. It is strongly magnetic, but only below about 20 °C, so on a warm day it loses its pull. And it soaks up neutrons better than any other stable element, which makes it useful for controlling nuclear reactors. In hospitals, gadolinium compounds are injected as contrast agents to make blood vessels and tumors stand out in MRI scans. The metal is wrapped in a molecular cage, because free gadolinium is toxic.