Here's why:

* Sand: Sand is primarily made up of silicon dioxide (SiO2), which is a compound containing silicon and oxygen.

* Rock: Many rocks contain silicon in various forms, including silicates. These minerals are essential components of granite, sandstone, and many other types of rock.

* Soil: Soil is formed from weathered rock, so it also contains silicon.

While silicon is a major component of sand, rock, and soil, it's important to note that other elements are also present in varying amounts.