Silicon, the Element That is Everywhere

A Natural Resource That Will Never Be in Short Supply

Nov 8, 2008

Throughout history, there has hardly been an era in which the technology did not depend on the non-metallic element silicon.

One reason for this is that silicon is everywhere. It makes up about 26% of the mass of the Earth’s crust, and is exceeded in abundance only by oxygen, with which it is invariably combined.

Most Rocks and Minerals Are Made of Metal Silicates

Igneous rocks, like granite, which are formed by the cooling of volcanic lavas, are composed mainly of crystals of quartz, feldspars and mica. The feldspars comprise the most abundant group of minerals and are five times as plentiful as quartz. They are made of aluminium silicates with varying amounts of potassium, sodium and calcium. Mica consists of thin, transparent, crystalline sheets. The high melting point and electrical resistance of mica make it useful in windows of stoves and furnaces and in electrical equipment.

Gemstones

Quartz is silicon dioxide in the form of large, white or colourless crystals. Flint is the same compound, but composed of microscopic crystals. Impurities in quartz give rise to coloured gemstones such as amethyst and opal. Banded forms of flint are found as the semi-precious onyx and agate. Other gems like topaz, emerald, zircon and garnet contain metals in addition to silicon.

Sedimentary and Metamorphic Rocks

Erosion of igneous rocks by wind, water and ice, breaks them into smaller fragments, and ultimately into sand and clay. Transport of these finer materials by rivers, followed by their deposition on lake and sea shores builds them up into layers, which slowly harden to the sedimentary rocks, sandstone and shale. If these are subjected to the high pressures and temperatures of volcanic activity, their crystalline structures change to those of the metamorphic rocks, quartzite, gneiss, schist and slate.

Biological Silicon

Silicon forms the basis of the skeletons of sponges and the tiny sea creatures known as diatoms, and gives strength to the stinging cells of nettles. It appears to have a role in bone structure and is found in human bodies to the extent of about one gram. Though it is non-toxic, its presence in rock dust can cause the lung disease silicosis in miners, while the needle-like structure of the magnesium silicate, asbestos, can damage lung tissue to the extent of causing cancer.

Silicon in the History of Chemistry

Despite the abundance and long usage of its compounds, silicon was first isolated as the pure element, by the Swedish chemist, Berzelius, as late as 1824. It is a member of a group, or family of elements that includes carbon, tin and lead.

The family resemblances are not immediately obvious. Carbon is non-metallic and mainly exists in the diverse forms of diamond, graphite and charcoal. Tin and lead are soft metals with low melting points. Silicon is a very hard, shiny non-metal with a high melting point. However, when Mendeleev proposed his structure for the Periodic Table of elements, in 1869, he used the similarities rather than the differences to predict the existence and properties of a fifth family member that was then unknown. When this element, germanium, was discovered in 1886, it was found to have the predicted properties, thus confirming Mendeleev’s theory.

The copyright of the article Silicon, the Element That is Everywhere in Inorganic Chemistry is owned by Anthony Toole. Permission to republish Silicon, the Element That is Everywhere in print or online must be granted by the author in writing.