Sima (geology)

In geology, sima (/ˈsaɪmə/) is an antiquated[1] blended term for the lower layer of Earth's crust.

This layer is made of rocks rich in magnesium silicate minerals.

Because the ocean floors are mainly sima, it is also sometimes called the 'oceanic crust'.

Comparable is the term sial (another antiquated blended term),[2] which is the name for the upper layer of Earth's crust (continental crust) , namely rocks rich in aluminium silicate minerals.

The most dense sima has less silica and forms ultramafic rocks.