Silicon dioxide (SiO₂)

Silicon dioxide (SiO₂)

A polymorphic compound, mostly found in the form of quartz.



silicon dioxide, quartz, sand, covalent network structure, gemstone, Quartz crystal, Amethyst, Flint, Agate, asbestos, glass, Glass manufacture, inorganic chemistry, chemistry

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Silicon dioxide SiO₂


Melting point: 1,703 °C (3,097.4 °F)

Boiling point: 2,230 °C (4,046 °F)

Density: 2.26 g/cm³ (0.0816 lb/in³)

Hardness: 7 (on the Mohs scale of mineral hardness)


Silicon dioxide exists in several varieties, all of which have diamond-like crystal structures. It occurs in the form of quartz in the largest volume. Quartz crystals are colorless, but small amounts of impurities color them. Quartz crystals are optically active.

Silicon dioxide is a very resistant substance; it does not dissolve in water, hydrochloric acid, sulfuric acid or other mineral acids. It breaks down in hydrofluoric acid (a solution of hydrogen fluoride in water). It dissolves well in hot bases and alkali hydroxides.

Occurrence and production

It occurs in large quantities in gneiss, mica slate, quartzite, sedimentary rocks and seams. Several varieties of quartz are considered gemstones, for example rock crystal, amethyst, chrysoprase, opal and jasper.


Silicon dioxide is used as an abrasive in the leather, wood, rubber, aluminium and steel industries. It is a raw material in the production of glass and ceramics. Due to its thermoluminescence it is also used to determine the age of ceramics.

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