Overall, the Earth is about 1.59% aluminium by mass. In the Earth's crust, aluminium is the most abundant metallic element by mass (8.23%). It is also the third most abundant of all elements in the Earth's crust. A lot of silicates in the Earth's crust contain aluminium. But, the Earth's mantle is only 2.38% aluminium by mass. Aluminium also occurs in seawater at a concentration of 2 μg/kg.