Glass and Crystal

Glass and crystals have many usages due to their special chemical and physical properties. They have very high melting points and unique optical properties. Both are very rigid material and have complex structures.

Glass

Glass is a solid inorganic material. Glass has a long history, which extends over the period of 3000 BC. There are evidences as to glass has been used at around 2500 BC, by the Egyptians. Glass has been used to make beads, mirrors, and windows back then; still it’s a material with a large number of applications. Glass is a hard material, but fragile, so it breaks into sharp pieces when fallen. Glass is primarily made with sand (silica/ SiO2), and bases like sodium carbonate, and calcium carbonate. At high temperatures, these materials melt together and when they are cooled, a rigid glass is formed rapidly. When cooling, the atoms are arranged in a disordered manner to produce glass; thus it is referred to as amorphous. However, atoms can have a short-range order due to chemical bonding characteristics. Normally, silica melts at about 2000 ^oC and the addition of sodium carbonate has reduced its melting point to 1000 ^oC. Depending on the added chemicals, type of glass varies. Usually, glass is transparent, and it could have colors according to the added material in the synthesizing process. It can refract, reflect,or transmit light, therefore, used to make lenses and windows. Glass doesn’t conduct electricity, but it can conduct heat. The reactivity of glass with different materials is minimum, thus, making it a good storing and packing material. It also doesn’t leach chemicals. Glass can withstand relatively high or low temperatures. With very high heat, it can be melted again, so it is easy to recycle.

Crystal

Crystals are solids, which have ordered structures and symmetry. The atoms, molecules or ions in crystals are arranged in a particular manner, thus, have a long range order. Crystals are naturally occurring on earth as large crystalline rocks, such as quartz, granite. Crystals are formed by living organisms too. For example, calcite is produced by mollusks. There is water based crystals in the form of snow, ice or glaciers. Crystals can be categorized according to their physical and chemical properties. They are covalent crystals (e.g.: diamond), metallic crystals (e.g.: pyrite), ionic crystals (e.g.: sodium chloride) and molecular crystals (e.g.: sugar). Crystals can have different shapes and colors. Crystals have an aesthetic value, also it is believed to have healing properties; thus, people use them to make jewelry.

What is the difference between glass and crystal? - Glass has an amorphous structure. That is, atoms in glass don’t have long range order, rather they have short range order. - Crystals have a long range order and atoms are arranged in a particular way. - Glass is formed when the heated silica is cooled rapidly. Since the glass is formed rapidly, the molecules don’t have enough time to rearrange orderly. If it’s allowed to cool slowly, crystals may form. - Usually, crystals are found naturally on earth, but glass is made.