What is "sial"

n. (context geology English) The rocks rich in silicon and aluminum that form the upper layer of the earth's crust, which lies beneath all continental landmasses.

n. the granite-like rocks that form the outermost layer of the earth's crust; rich in silicon and aluminum

In geology, the sial refers to the composition of the upper layer of the Earth's crust, namely 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 than the majority of the earth's elements, 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 nickel-iron alloy core, sometimes referred to as the "Nife". These geochemical 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.

Sial may refer to:

• Sial the composition of the upper part of the Earth's crust
• Sial (tribe), a people of Pakistan
• SIAL, the consortium which runs Sialkot International Airport