Here's why:

* Silicon is the second most abundant element in the Earth's crust. It's a major component of minerals that make up rocks.

* Silicate minerals are the most common type of mineral. These minerals are made up of silicon and oxygen, often combined with other elements like aluminum, iron, calcium, magnesium, and potassium.

Here are some examples of common rocks containing silicon:

* Granite: A hard, igneous rock rich in quartz (silicon dioxide).

* Basalt: A dark, volcanic rock with significant amounts of silicate minerals.

* Sandstone: A sedimentary rock formed from sand grains, which are mostly made of quartz (silicon dioxide).

* Quartzite: A metamorphic rock formed from sandstone with high quartz content.

* Feldspar: A very common mineral found in many rocks, containing silicon, aluminum, and other elements.

Exceptions:

While most rocks contain silicon, there are some exceptions. These include:

* Limestone: A sedimentary rock primarily made of calcium carbonate, with very little silicon.

* Gypsum: A sedimentary rock primarily made of calcium sulfate, with very little silicon.

Overall, it's safe to say that silicon is a major building block of most rocks on Earth.