10 Most Abundant Compounds in the Earth's Crust

Silicon dioxide                   SiO2                           42.86% 428,600

Magnesium oxide                         MgO                           35.07% 350,700
Ferrous oxide                    FeO                            8.97% 89,700
Aluminum oxide              Al2O3                       6.99% 69,900
Calcium oxide                    CaO                            4.37% 43,700
Sodium oxide                     Na2O                         0.45% 4,500
Ferric oxide                        Fe2O3                       0.36% 3,600
Titanium dioxide              TiO2                          0.33% 3,300
Chromic oxide                   Cr2O3                       0.18% 1,800
Manganese dioxide                     MnO2                        0.14% 1,400

Source : Exploring Chemical Elements and their Compounds Compound Formula Abundance percent by weight Abundance

parts per million by weight