The crust of the earth contains only eight elements (oxygen, silicon, aluminum, iron, calcium, sodium, potassium, and magnesium) with concentrations greater than l% by weight. Minerals are compounds of these elements. each mineral having a specified crystalline structure. The most abundant minerals represent only five types of chemical compounds: silicates, carbonates, sulfates, halides, and oxides. Of these minerals, the silicates are more abundant than all the rest combined, comprising 95% of the rest.