Boron is a metalloid element (more non metal then metal) with chemical symbol B and atomic number 5. It is solid and black at normal pressure and temperature, it is easily to break with a hammer. Boron is not a very frequent element and is found in nature only in compounds together with oxygen. Crystalline Boron, which is shown here, is nearly as hard as diamond (9.5 on Mohs scale, diamond has 10). Boron has a different biological functions. Boron compounds have many, often very special applications, a common one is B2O3 for borosilicate glass. Most famous are the perborates as bleach and as washing agent. Because of their bad biodegradability the use of perborates has gone back.