What is the Composition of the Earth's Crust?

The Earth's crust is primarily composed of silicate minerals, with oxygen and silicon as the most abundant elements. Let's break down the composition in more detail:

Eight elements make up over 99.5% of the Earth's crust by weight:

• Oxygen (O): 46.6%
• Silicon (Si): 27.72%
• Aluminum (Al): 8.13%
• Iron (Fe): 5.00%
• Calcium (Ca): 3.63%
• Sodium (Na): 2.83%
• Potassium (K): 2.60%
• Magnesium (Mg): 2.08%

While 93 elements are present, these eight dominate the overall mass.

Mineral Composition

More than 90% of the crust consists of silicate minerals. The most prevalent are:

• Feldspars: These are the most abundant minerals, with plagioclase feldspar making up approximately 39% and alkali feldspar comprising about 12% of the crust.

Other significant minerals include quartz, pyroxenes, amphiboles, micas, and olivine, each contributing to the overall rock types found in the crust.

Crustal Types and Variations

It's crucial to note that the crust is not uniform in composition. There are two main types:

• Continental Crust: This is thicker and less dense, predominantly composed of felsic (rich in feldspar and silica) rocks like granite. The lower continental crust can be more mafic (rich in magnesium and iron), approaching the composition of basalt.

• Oceanic Crust: This is thinner and denser, primarily composed of mafic rocks like basalt.

The specific composition can vary significantly based on location and geological processes. Factors such as volcanic activity, tectonic plate interactions, and weathering influence the local mineral and elemental proportions.