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Noah Rand

Physical Geology

Autumn 2008


The many applications of silica & silicates


     Silicon dioxide (silica) is an oxide of silicon. The surface of silicon oxides when exposed to oxygen forming SiO2. From the Latin silex for hard stone.

     Of all the the different chemical compounds and minerals on our Earth's crust, silicon dioxide is the most plentiful and ubiquitous of all making up 60 percent of it. It comes in many natural forms such as quartz, sand, cristobalite, jasper, chalcedony, tridymite, agate, stishovite, opal, coesite, radiolarite, lechatelierite, and the cell walls of diatoms. Lucky for us silica has many uses and applications which help and impact our daily lives.



     Quartz is one of the most common crystalline form of silicon dioxide. Chert is a cryptocrystalline variety of quartz with many varieties itself such as onyx, opal, jasper, agate and flint. Agate was once used to make mortars & pestles as well as being used for leather burnishing. Flint once had many uses as a cutting utensil, ignition tool, building material. Now these natural quartz are used less and less. Naturally occurring quartz and its many major varieties have many uses and are very beautiful and made into lovely jewelry but most of the material used for industrial and commercial applications today are processed or synthetic quartz or a quartz analogic. One such application is the tiny piece of quartz used in a wristwatch as a piezoelectric oscillator to create precise frequency in order to keep time much more accurate than mechanical timekeeping. Watch manufacturers exclusively use synthetic quartz for their quartz wristwatches.


     Another form of quartz is fused quartz/silica. Naturally occurring quartz of high purity is melted at 2000C to make clear fused quartz glass or fumed silica powder. Fumed silica powder has many application as a filler or additive. In solids, it aids flow due to its submicron particles. In other powders, it prevents caking by absorbing water off the surface of particles. In liquids, it aids flow and permit the escape of entrapped air through its chain-like particle morphology and thixotropy. Clear fused quartz has even more uses than fumed silica. Clear fused quartz transmits 92% of the light passed through it making it ideal for all sorts of optical and light-related applications including but not limited to: 

          lenses for optical instruments in astronomy (such as the reference telescope in The Gravity Probe B experiment), photography and cinematography, fiber optics for telecommunications

     Not only that fused quartz's high melting pointing and its stability in temperature fluctuations make it ideal for various different temperature related applications such as:       

         beaker and thermometers, halogen lamps for lighting


     Fused quartz also has good dielectric and insulating properties and has very high tensile strength.


Sand & Diatomite

     Sand is naturally occurring, granular material usually made of silica in the form of quartz. While diatomite is chalky, very fine-grained, sedimentary rock made of varying levels of silica (usually at least 85%) from the siliceous cell walls of fossilized diatoms.


     Sand is a primary ingredient in concrete. Used as a fine aggregate in concrete mixtures it helps give the finished product its stone-like hardness. In much the same manner, it is added to certain types of bricks and is also used to make the mortar to hold the bricks together. Along with these chemical uses of sand there is also the use of sand in sand bags, sand blasting, sand casting, beach nourishment, flux sand for iron and steel making,


     Due to fine porosity, diatomite is used for filtration of swimming pool, of very fine particles in chemistry, of drinking water, and various industrial products. It has also been used as a mild abrasive in toothpaste and facial scrubs as well as a natural insecticide due to its sorptivity and as cat little due to its absorbent quality.



     The simple molecular formula of SiO2 has not only shaped the wondrousness of the world of nature but it has also populated and informed the human worlds of culture and commerce. It helps the contemporary world we live in flow a little bit more easily and for that alone we shouldn't ignore what may be a mundane and boring little mineral.