Germanium is a chemical element with symbol Ge and atomic number 32. It is a lustrous, hard, grayish-white metalloid in the carbon group, chemically similar to its group neighbors tin and silicon.
GW 963 (OTTO) Germanium optical windows, 70 mm dia,15 mm thick, 99.999% - used at temperatures below 100°C. Germanium’s high density (5.33 g/cm3) should be considered when designing for weight-sensitive systems