Silica and Alumina
Explanation
The Earth's crust is the outermost solid shell of the planet and is chemically distinct from the underlying mantle. It is broadly classified into two types based on composition and thickness: Continental Crust and Oceanic Crust.
- Continental Crust (SIAL): The main mineral constituents of the continental mass are Silica and Alumina. Consequently, it is often referred to as SIAL (taken from the first two letters of Silica and Alumina). It is generally thicker and less dense than the oceanic crust.
- Oceanic Crust (SIMA): The main mineral constituents of the oceanic crust are Silica and Magnesium. It is therefore called SIMA (Si from Silica and Ma from Magnesium). It is thinner and denser than the continental crust.
- Core (NIFE): The innermost layer of the Earth is composed mainly of Nickel and Iron, referred to as NIFE.
Key Takeaway: The continental crust is primarily felsic in nature, dominated by Silica and Alumina (SIAL), whereas the oceanic crust is mafic, dominated by Silica and Magnesium (SIMA).