Here's why:

* Oxygen is a highly reactive element and readily forms compounds with other elements.

* Silicates, the most abundant group of minerals, are composed primarily of silicon and oxygen. These minerals make up a large portion of the Earth's crust and mantle.

* Oxides are also common minerals, containing oxygen bonded with other elements like iron, aluminum, and calcium.

* Water, a crucial component in many geological processes, is also composed of hydrogen and oxygen.

While other elements like silicon, aluminum, and iron are also abundant in rocks and minerals, oxygen takes the top spot in terms of overall percentage.