Silicon is a grey colored element with crystalline structure. It is the second most abundant element in the earth's crust, after oxygen. Silicon is always found in combined form in nature, often with oxygen as quartz, and is found in rocks and silica sand. To be able to use silicon as a semiconductor, in for example a transistor, it needs to be in a very pure form. If there is more than one impure particle in a million, the silicon can not be used. Silicon is the most frequently used semiconducting material today.