A generic term for the rocks making up the upper half of the Earth's crust, so called because
Silicon and
aluminum predominate. Sial is also commonly referred to as "
Granitic rock".
Sial sits on top of a denser, "
basaltic" layer, called
Sima (because
silicon and
magnesium predominate).
I can't find who originally coined "sial" and "sima", but the terms are frequently associated with
Alfred Wegener, as the
isostatic balance between Sial and Sima is one of the fundamental parts of his theory of
continental drift.