Geol. the heavy igneous rock material of the earth's inner crust, forming a continuous shell and underlying the sial and also the ocean floors
Origin of simaGerman from si(licium), silicium + ma(gnesium), magnesium
The lower layer of the earth's outer crust that underlies the sial and is rich in silica, iron, and magnesium.
Origin of simasi(lica) ma(gnesium)
From the Ancient Greek "simos" (bent upwards)