What is it?
“First of all, silicone is no more “natural” than fossil-based plastic. It is a man-made polymer, but instead of a carbon backbone like plastic, it has a backbone of silicon and oxygen. (Note that I’m using two different words here: silicone is the polymer and silicon, spelled without the “e” on the end, is an ingredient.)
Silicon is an element found in silica, i.e., sand, one of the most common materials on earth. However, to make silicone, silicon is extracted from silica (it rarely exists by itself in nature) and passed through hydrocarbons to create a new polymer with an inorganic silicon-oxygen backbone and carbon-based side groups.
So while the silicon might come from a relatively benign and plentiful resource like sand, the hydrocarbons in silicone come from fossil sources like petroleum and natural gas, so is a kind of hybrid material.” (Terry, p. 277)