sial

thumb|right|250 px|Typical sial material, a Precambrian [[granite from St. Francois Mountains, Missouri, showing the potassium feldspar (felsic) matrix]]

In geology, sial is an antiquated blended term for the composition of the upper layer of Earth's crust, namely rocks rich in aluminium silicate 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 Earth's elements, they tend to be concentrated in the upper layer of the crust.