Chemical Composition of the Earth's Crust

This table shows the chemical composition or abundance of chemical compounds in the Earth's crust. As you can see, the most common compound in the Earth's crust is silica. Quartz consists of silica and it is the primary constituent of most sand.

Reference: Brown, Geoff C.; Mussett, Alan E. (1981). The Inaccessible Earth (2nd ed.). Taylor & Francis. p. 166.

Compounds in the Earth's Crust

Compound	Formula	Continental % Composition	Oceanic % Composition
silica	SiO2	60.2	48.6
alumina	Al2O3	15.2	16.5
lime	CaO	5.5	12.3
iron(II) oxide	FeO	3.8	6.2
magnesia	MgO	3.1	6.8
sodium oxide	Na2O	3.0	2.6
potassium oxide	K2O	2.8	0.4
iron(III) oxide	Fe2O3	2.5	2.3
water	H2O	1.4	1.1
carbon dioxide	CO2	1.2	1.4
titanium dioxide	TiO2	0.7	1.4
phosphorus pentoxide	P2O5	0.2	0.3
Total		99.6%	99.9%