What is Silicon Dioxide?

Silicon Dioxide Clearly Explained

Silicon dioxide, also known as silica, is a compound of two of the most abundant chemical elements in Earth's crust, silicon (Si) and oxygen (O).

Made up of one atom of silicon and two of oxygen, the chemical formula for silicon dioxide is SiO₂. 

Silicon dioxide is most commonly found in nature as the mineral quartz. It's present in sand and soil, and is also found in water and living organisms.

Silicon dioxide exists in many crystalline and cryptocrystalline forms, but it can also be non-crystalline.

In its purest form, the crystalline form of silicon dioxide (quartz) is colourless and transparent. However, impurities can introduce many different colours.

Cryptocrystalline varieties are generally known as chalcedony. Examples include agate, carnelian, chrysoprase, and onyx. 

Because the names silicon and silicon dioxide are so similar, these two substances are often confused.

Both names come from the same root word.

The shared part of the name identifies the main component, silicon.

The word “dioxide” simply means:

• di- = two
• oxide = oxygen

So silicon dioxide literally means silicon + two oxygen atoms.

Here are the key differences between the two:

Silicon dioxide is widely used in industry because its melting point is higher than that of copper, iron, and aluminium.

It's used in the production of glass, optical fibres and as a raw material in whiteware ceramics, stoneware, porcelain, and industrial cement. Silicon dioxide is also used in toothpaste because its hardness helps remove plaque.

As a food additive, silicon dioxide protects dried foods from moisture and powdered foods from clumping or sticking together. 

The small white packets called silica gel, often found with new merchandise, contain silicon dioxide, which absorbs moisture and helps protect whatever they're packed with.

Origins of the Name "Silica"

The word silica comes from the Latin word silex, which means flint or hard stone.

Historically, silica was the traditional name used for materials such as flint, quartz, and sand long before modern chemistry existed.

When chemistry later identified their composition, these materials were found to be silicon dioxide (SiO₂).

Silica remained in use as the common, everyday name, while silicon dioxide became the formal chemical name.

Silica = traditional, historical name
Silicon dioxide = scientific, chemical name

Both refer to the same substance.

Article Photos

The quartz at the top of our article is from our collection. 

Pop-up photos
Agate slices: From our collection. Chrysoprase: Courtesy of James St. John. Flint: Courtesy of Stan Celestian.