Silicon, Silica, and Silicone

2019-06-18 lixingdotcom Materials Science Fundamentals Leave a comment

Silicon(Silicon)

Silicon is the second most abundant element in the Earth's crust. The source describes approximately 27% of rock material as silicon and 55% as silicon combined with oxygen. Silica, or silicon dioxide, is one of the most common silicon–oxygen compounds.

Silicates (Silica)

Silicates are a broader category of silicon–oxygen compounds (SixOy). Quartz is silicon dioxide; tridymite, coesite, cristobalite, and quartzite are also listed in the source as forms of silica.

Quartz consists of pure silicon dioxide. Feldspars contain sodium, aluminum, potassium, or calcium in addition to silicon and oxygen, so they are silicate minerals rather than pure silica.

Geologists sometimes use silica to describe the total silicon content of a rock expressed as silicon dioxide. This can be confusing. In rock analysis, the silicon content of a dissolved sample may be determined by precipitating silica. A geologist might therefore say a rock contains 48% silica even when no quartz is visible. Both observations can be valid: silicon and oxygen may be combined with other elements in silicate minerals such as feldspar. It is like looking at a cake and saying no eggs are visible—the eggs are present in a different form.

Silicone (Silicone )

Silicone is a synthetic polymer containing carbon and oxygen that can be solid, liquid, or gel-like. It has medical uses, including acid-resistant applications, artificial joints, and pacemakers, but is not found in rocks as some people assume. Pure silicon can occur naturally, although it is rare.

Russian geologists collected gases at Kudryavy volcano by placing quartz tubes in vents emitting gas above 900°C. Minerals precipitated inside the tubes, including silicon-containing crystals up to 0.3 mm across, described as Si–Al alloy. Unless sampling hot volcanic gases, naturally encountered materials are generally silica and silicates rather than silicon or silicone.