Since my theme is all things scifi, I had to include silicon, a key element of computer chips (although in researching this I came across a possible replacement...).
But what exactly is silicon, you might ask? Well, let me explain... Silicon is a chemical element and according to Wiki, the eighth most common element in the universe (although since we haven't actually explored the entire universe quite yet, I wonder how anyone could prove that claim...) and the second most plentiful element in the earth's crust. However, it is purified silicon that is used in semiconductor electronics and integrated circuits, and in fact, modern technology depends upon it.
Do you think we'll find a replacement?