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)