[ sahy-muh ]
/ ˈsaɪ mə /

noun Geology.

an assemblage of rocks, rich in silica and magnesium, that constitutes the lower layer of the earth's crust and is found beneath the ocean floors and the sial of continents.

Origin of sima

< German (1909), equivalent to Latin si(licium) silicium + ma(gnesium) magnesium

Related forms

si·mat·ic [sahy-mat-ik] /saɪˈmæt ɪk/, adjective Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

British Dictionary definitions for simatic


/ (ˈsaɪmə) /


the silicon-rich and magnesium-rich rocks of the earth's oceanic crust, the most abundant individual rock being basalt
the earth's continental lower crust, probably comprised of gabbro rather than basalt

Derived Forms

simatic (saɪˈmætɪk), adjective

Word Origin for sima

C20: from si (lica) + ma (gnesia)
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012