In its oxide or silicate form, silicon is used to make concrete, bricks, glass, ceramics, and soap. Silicon metal is also the base material for making silicones used in such products as synthetic oils, caulks and sealers, and anti-foaming agents.
Intrusive igneous rocks crystallize below Earth's surface, and the slow cooling that occurs there allows large crystals to form. Examples of intrusive igneous rocks are diorite, gabbro, granite, pegmatite, and peridotite. Extrusive igneous rocks erupt onto the surface, where they cool quickly to form small crystals.
Plutonic rocks, which cool slowly underground, have large crystals because the crystals had enough time to grow to a large size. Volcanic rocks, which cool quickly above ground, have small crystals because the crystals did not have enough time to grow very large. The type of igneous rock is also dependent on its composition (the elements that are present). There are many different compositions of magma and lava. Fortunately, most igneous rocks are one of three basic compositions: 1  Felsic igneous rocks contain relatively high amounts of silicon, sodium, aluminum, potassium (Si, Na, Al, and K) and relatively low amounts of iron, magnesium, and calcium (Fe, Mg, Ca).