1. Oxygen (O) - Makes up about 46.6% of the crust by weight.

2. Silicon (Si) - Makes up about 27.7% of the crust by weight.

These two elements combine to form the most abundant mineral group: silicates.

Silicates are a diverse group of minerals, and they make up about 90% of the Earth's crust. They are characterized by the presence of the silicate tetrahedron (SiO4)4-. This tetrahedron can link together in various ways, leading to a wide variety of silicate minerals. Some common examples include quartz, feldspar, and mica.