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.
Extrusive Igneous Rocks â¢Extrusive igneous rocks form when magma makes its way to Earth's surface. The molten rock erupts or flows above the surface as lava, and then cools forming rock. â¢Most extrusive (volcanic) rocks have small crystals. Examples include pumice, obsidian, and basalt.