There are several different kinds of rock formations that make up the Earth's topmost terrain layer.
The most common elements in the Earth's crust are the rock-forming elements, chiefly oxygen mixed with silicon. Because of its prevalence in the atmosphere, all organic matter and the various bodies of water, oxygen may be the most abundant single element present on Earth's surface. However, there are many elements that exist in the Earth's crust that are vital to industry.
Silicon
Silicon (Si) is the most common metalloid on earth, comprising about 28 percent of the Earth's crust. It is the seventh most abundant element in the known universe. Silicon is used prominently in semiconductors, glass, cement and ceramics. Beach sand, incidentally, is mostly made up of silicon.
Aluminum
Aluminum (Al) is the most common metal on earth, comprising about 8 percent of the Earth's crust. It is especially useful in industrial applications in which a strong, light metal is needed, and is used in applications from foil to tank armor. Despite its abundance, no known lifeforms use aluminum in a dietary or organic manner.
Iron
Iron (Fe) is the second most abundant metal in Earth's crust, comprising 5 percent of the total composition. Unlike oxygen, it is extremely prevalent in the interior of the Earth, making it the most prevalent material on all of Earth. It has been used by humans for thousands of years to make weapons and work instruments. The Iron Age is the last prehistoric age before the oldest civilizations emerged.
Calcium
Calcium (Ca) comprises about 4 percent of the Earth's crust and is the fifth most abundant mineral in seawater. Like iron, it is essential to living organisms, particularly in the makeup of bone and shell material. Calcium is used in industrial and agricultural applications such as quicklime and slaked lime.
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