Beryllium

Beryllium (Be) is a steel-gray alkaline earth metal that combines low weight with high stiffness, although it is brittle. In nature, it is bound to other elements in minerals, especially the ores beryl and bertrandite. Emerald and aquamarine are gemstone varieties of beryl. To obtain the metal, producers chemically process the ores, separate out beryllium compounds, and typically use magnesium to extract beryllium from its fluoride. Its low weight and ability to hold its shape in extreme cold make it useful for the gold-coated mirrors of the James Webb Space Telescope. Thin beryllium sheets also serve as windows in X-ray equipment because X-rays pass through them easily. Breathing beryllium-containing dust can cause serious lung disease.