Germanium ( /dʒərˈmeɪniəm/ jər-may-nee-əm) is a chemical element with the 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. The isolated element is a semiconductor, with an appearance most similar to elemental silicon. Like silicon, germanium naturally reacts and complexes with oxygen in nature. Unlike silicon, it is too reactive to be found naturally on Earth in the free (native) state.
Germanium was discovered comparatively late in the history of chemistry, because very few minerals contain it in high concentration. Germanium ranks near fiftieth in relative abundance of the elements in the Earth's crust. In 1869, Dmitri Mendeleev predicted its existence and some of its properties based on its position on his periodic table and called the element eka-silicon. Nearly two decades later, in 1886, Clemens Winkler found that experimental observations agreed with Mendeleev's predictions and named the element after his country, Germany. Today, germanium is mined primarily from sphalerite (the primary zinc ore), though germanium is also recovered commercially from silver, lead, and copper ores.
Germanium "metal" (isolated germanium) is used as semiconductor in transistors and various other electronic devices. Historically the first several decades of semiconductor electronics were entirely based on germanium, although its production for such use today is a small fraction (2%) of that of ultra-high purity silicon, which has largely replaced it. Germanium's major end uses in the present are fiber-optic systems and infrared optics. It is used in solar cell applications. Germanium compounds are used for polymerization catalysts. Germanium is finding a new use in nanowires. Germanium forms a large number of organometallic compounds, such as tetraethylgermane, which are useful in chemistry.
Germanium is not thought to be an essential element for any living organism. Some complexed organic germanium compounds are being investigated as possible pharmaceuticals but none has had success. Similar to silicon and aluminum, natural germanium compounds, which tend to be insoluble in water, have little oral toxicity. However, synthetic soluble germanium salts are nephrotoxic, and synthetic chemically-reactive germanium compounds with halogens and hydrogen, are irritants and toxins.