Chinese researchers have developed an environmentally friendly method to extract caesium from brine, a process they say could boost China’s supply of the strategic resource. Caesium, a rare metal, is a critical strategic resource used in satellite atomic clocks, missile thermal imaging sensors and advanced speciality glass. China and the United States are the top consumers of caesium, yet both rely heavily on imports. It is primarily found in the Earth’s crustal ores as well as salt lake brines.