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 one or more of these oxygen atoms replaced by another element. These compounds can crystallize, which is the basic material in numerous minerals that are also referred to as silicates. The atoms in place of oxygen 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.