Beryllium (pronounced) is the chemical element with the symbol Be and atomic number 4.
A bivalent element, beryllium is found naturally only combined with other elements in minerals. Notable gemstones which contain beryllium include beryl (aquamarine,emerald) and chrysoberyl.
The free element is a steel-grey, strong, lightweight brittle alkaline earth metal. It is primarily used as a hardening agent in alloys, notably beryllium copper. Structurally, beryllium's very low density (1.85 times that of water), high melting point (1278 °C), high temperature stability, and low coefficient of thermal expansion, make it in many ways an ideal aerospace material, and it has been used in rocket nozzles and is a significant component of planned space telescopes. Because of its relatively high transparency to X-rays and other ionizing radiation types, beryllium also has a number of uses as filters and windows for radiation and particle physics experiments.
Commercial use of beryllium metal presents technical challenges due to the toxicity (especially by inhalation) of beryllium-containing dusts. Beryllium produces a direct corrosive effect to tissue, and can cause a chronic life-threatening allergic disease called beryllionis in susceptible persons.
Beryllium is a relatively rare element in both the Earth and the universe, because it is not formed in conventional stellar nucleosynthesis, but rather during the Big Bang, and later from the action of cosmic rays on interstellar dust. The element is not known to be necessary or useful for either plant or animal life.
source from : http://en.wikipedia.org/wiki/Beryllium
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