silicate

The term silicate is used for compounds that include a certain configuration of silicon and oxygen atoms, i.e., a silicon atom bound to four oxygen atoms, or with an atom of some other element in place of one or more of these four oxygen atoms. These compounds can crystallize, which is the basic material in numerous minerals that are also referred to as silicates. The atoms in place of the oxygen atoms can be metals (metal as per chemistry, e.g., aluminum or iron).

What we call rock, including much of the Earth's crust and mantle are basically silicates. Rocky planets are presumed to be similar to Earth in this respect, including extra-solar planets with densities suggestive of a similar makeup.