Basic uses of silica:
　　Silica is the raw material for manufacturing glass,quartz glass,water glass,Optical fiber,important parts of electronic industry,Optical instrument,handicrafts and refractory materials,and is an important material for scientific research.
　　The use of silica:flat glass,glass products,casting sand,glass fiber,ceramic glaze,sandblasting for rust prevention,sand for filtration,flux,refractory materials,and the manufacturing of Autoclaved Lightweight Concrete.Silicon dioxide has a wide range of uses.Rare crystals in nature can be used to manufacture important parts of electronic industry,Optical instrument and handicrafts.Silica is an important raw material for manufacturing Optical fiber.Generally pure quartz can be used to make quartz glass.Quartz glass has a small expansion coefficient,equivalent to 1/18 of ordinary glass,and can withstand temperature fluctuations.It has good acid resistance(except for HF),so quartz glass is often used to manufacture high-temperature resistant chemical instruments.Quartz sand is commonly used as a raw material for glass and building materials.
　　Physical and chemical properties:
　　Silicon dioxide,also known as silica,has the chemical formula SiO₂.There are two types of silica in nature:crystalline silica and amorphous silica.
　　Crystalline silica is divided into three types due to its different crystal structures:quartz,tridymite,and cristobalite.Pure quartz is a colorless crystal,and large and transparent prismatic quartz is called crystal.If the crystal containing trace impurities has different colors,there are Amethyst,tea crystal,ink crystal,etc.Ordinary sand is small quartz crystals,consisting of yellow sand(with more iron impurities)and white sand(with less impurities and relatively pure).In the silicon dioxide crystal,four Valence electron of silicon atom form four Covalent bond with four oxygen atoms.The silicon atom is located in the center of the Regular tetrahedron,and four oxygen atoms are located at the four top corners of the Regular tetrahedron.Many such tetrahedrons are connected by the oxygen atoms at the top corners.Each oxygen atom is shared by two tetrahedrons,that is,each oxygen atom is combined with two silicon atoms.SiO₂is the simplest formula for composition,which only represents the ratio of the number of atoms of silicon and oxygen in silicon dioxide crystals.Silica is a Network covalent bonding.
　　The bond energy of the Si-O bond in SiO₂is very high,with high melting and boiling points(melting point 1723℃,boiling point 2230℃).The refractive index is approximately 1.6
　　The refractive index of various silica products is 1.547 for quartz sand;1.544 for powdered quartz;Vein quartz is 1.542;Diatomaceous earth ranges from 1.42 to 1.48;1.46 for fumed silica;Precipitated silica is 1.46.
　　Diatomaceous earth in nature is amorphous silicon dioxide,which is the remains of lower Aquatic plant diatoms.It is a white solid or powder,porous,light,soft solid with strong adsorption.
　　chemical property
　　The chemical properties are relatively stable.It is insoluble in water and does not react with water.It is Acidic oxide and does not react with ordinary acid.Gaseous hydrogen fluoride reacts with silica to form gaseous Silicon tetrafluoride.React with a hot concentrated alkali solution or molten alkali to produce silicates and water.React with various metal oxides at high temperatures to form silicates.Used for manufacturing quartz glass,Optical instrument,chemical utensils,ordinary glass