Here's why:

* Silicate minerals are the most common type of minerals found in the Earth's crust and mantle, which are the sources of magma and lava that form igneous rocks.

* Silicon and oxygen are the most abundant elements in the Earth's crust, and they readily bond to form silicate minerals.

* Common silicate minerals found in igneous rocks include quartz, feldspar, mica, pyroxene, and amphibole.

While there are some exceptions, the vast majority of igneous rocks are primarily composed of silicate minerals.