Silica that exists in nature is collectively called silica, and there are two types: crystalline and amorphous. Quartz crystals are crystalline silica. Among them, pure and transparent quartz is called crystal, which presents different colors according to different trace impurities. For example, purple amethyst, brown smoky quartz, agate and jasper are also quartz with impurities. The sand usually seen is quartz with more impurities: diatomaceous earth is amorphous silicon dioxide.

(1) In the silicon dioxide crystal, silicon atoms and oxygen atoms are combined to form a regular tetrahedral spatial network structure. Each silicon atom is combined with 4 adjacent oxygen atoms. The silicon atom is in the center of the regular tetrahedron, and the oxygen atom is in the center of the regular tetrahedron. On the four vertices of the regular tetrahedron, the ratio of the number of silicon and oxygen atoms is 1:2.

(2) Silica is chemically inactive at room temperature. ① Silica can react with lye and HF acid at room temperature. ② Silica is an acidic oxide and can react with alkaline oxides at high temperature. ③ High temperature. Lower silica can react with certain salts.

(3) Silica has many uses. ① It is often used in important parts of the electronics industry, optical instruments and handicrafts (crystals, agate, etc.), ② making optical fibers (optical cables), ③ making quartz glass, ④ quartz sand is often used in making Glass and building materials, ⑤ Diatomaceous earth is used as catalyst carrier and adsorbent.