Sial

In geology, the sial is the upper layer of the Earth's crust made of rocks rich in silicates and aluminium minerals. It is sometimes equated with the continental crust because it is absent in the wide oceanic basins, but "sial" is a geochemical term rather than a plate tectonic term. As these elements are less dense, they tend to be concentrated in the upper layer of the crust.

Geologists often refer to the rocks in this layer as felsic, because they contain high levels of feldspar, an aluminium silicate mineral series. However, the sial "actually has quite a diversity of rock types, including large amounts of basaltic rocks."

The name 'sial' was taken from the first two letters of silica and of aluminium. The sial is often contrasted to the 'sima,' the next lower layer in the Earth, which is often exposed in the ocean basins; and the nife, the nickel-iron core. These divisions of the Earth's interior (with these names) were first proposed by Eduard Suess in the 19th century. This model of the outer layers of the earth has been confirmed by petrographic, gravimetric, and seismic evidence.