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.
How igneous rocks are used Igneous rocks are formed deep inside Earth's crust (intrusive rocks) or at the surface (extrusive rocks). As molten rock (known as magma) below the surface cools, the liquid material begins to solidify into minerals of differing sizes and compositions. Generally, the longer the cooling time, the larger the mineral crystals can grow.