Silicon was one of many elements in the galaxy. It bonded with oxygen to make silica and quartz. Silicon shared some of the same properties of carbon, and was the only possible rival for the role of carbon in biology. However, silicon could only bond with two other atoms, whereas carbon could bond with up to four other atoms at once, and was therefore able to form long molecular chains and rings, the backbones of organic molecules. Because of the limitations of silicon, silicon-based lifeforms were extremely rare.