The most striking thing you notice about this metal is how absurdly light it feels in hand. While lithium is lighter it is, frankly, useless as a metal proper because it's soft enough that you can wrap a rod of it around your fingers. Worse, it’s so reactive that it tarnishes within seconds of exposure to air and quickly corrodes into a pile of dust. Beryllium on the other hand has neither of those two properties. But - there’s always a but - it’s hideously expensive and difficult to work with. Only a few companies in the world have the expertise to work with this metal. 

Much also has been said about its toxicity. A lungful of beryllium dust is bad, bad news. Pulmonary edema, or close to it, is the lifelong diagnosis of berylliosis. But then again, you really don't want a lungful of any metal dust. If you can avoid the questionable temptation to take a file to your precious little piece of beryllium then you have nothing to worry about. As a solid piece of metal it poses no more or less danger than the keys in your pocket. It has been reported, however, that a minority of people have an allergic reaction to beryllium metal on their skin. While it is thought that it is, again, the fine dusts that trigger this response, if you are the type who for whatever reason enjoys constantly fondling your beryllium bits and you start getting all itchy and stuff maybe… you know… stop?

CAS 7440-41-7