The oceanic crust is composed of dark, iron-rich rock similar to basalt. It is high in silica and magnesium, that is why called SIMA. It is often distinguished from the mantle by having more silica. This implies that Oceanic crust is more basaltic. Since Magnesium is denoted by Mg and Iron is denoted by Fe, these rocks have also been named Mafic Rocks. Most common rock-forming Mafic minerals in the oceanic crust are olivine, pyroxene, amphibole, and biotite.
- The continental crust’s composition is more complex. In general, continental rocks are light-colored, with an average composition between diorite (generally hornblende and plagioclase feldspar with a little quartz) and granodiorite (the same composition as diorite, but with more quartz present). These are rocks high in silica and aluminium and are often referred to as This implies that Continental crust is more felsic.
- Then, there is a difference in density also. The oceanic crust has a density of 3,000 kilograms/m³ while the continental crust has a lower density of 2,500 kilograms/m³. This also implies that the rocks which make continental crust are slightly less dense than those making the Oceanic Crust. The less dense rocks such as granite is more common in continental crust than in oceanic crust. Density of Sial is lower than Sima primarily because of the increased amount of aluminium.
- Please note that at a certain depth, the SIAL of the Continental Crest becomes close in its physical properties to SIMA.
- The temperature of the crust increases with depth, reaching values typically in the range from about 200-400°C at the boundary with the underlying mantle.