Emerald is a rare gem containing beryllium.
Beryllium is strong and light, which makes it a useful material in space. The large mirror on the James Webb Space Telescope is made of beryllium coated with a thin layer of gold.
Beryllium is highly transparent to X-ray, and it can be used as radiation windows for X-ray equipments.
Beryllium dust is poisonous. Inhalation of beryllium dust can cause lung disease.
Strong and non-sparking tools can be made with beryllium copper, an alloy with beryllium less than 3%.
