Question

the layer of lithosphere which is made up of silicon and magnesium ​

Answer 1

In geology, sima (/ˈsaɪmə/) is an antiquated blended term for the lower layer of the Earth's crust. This layer is made of rocks rich in magnesium silicate minerals.

Answer 2

At close to 3,000 kilometers (1,865 miles) thick, this is Earth's thickest layer. It starts a mere 30 kilometers (18.6 miles) beneath the surface. Made mostly of iron, magnesium and silicon, it is dense, hot and semi-solid (think caramel candy).