The origin of the word crystal lies in the Greek word ‘Krustallos,’ which means ice as well as rock crystal.Interestingly, the ancient Greeks thought clear quartz crystals to be ice that doesn’t melt. Today, thanks to science, we know that a crystal is not frozen ice, but a mineral rock.The scientific definition of crystal says that it is a solid material characterized by its building atoms, occurring in a definite recurring pattern and arrangement. The molecular structure of a crystal is well organized and is as vital as the molecules it contains for determining its properties. At a macroscopic level, crystals have a characteristic geometric shape with specific flat surfaces and orientations.The process through which crystals are formed is called crystallization. The branch of science that delves into the details of crystals, their formation, and growth is called crystallography.Do you know most minerals occur in nature in the form of crystals? Apart from the semi-precious gems, and precious stones like quartz, amethyst, and diamond, we know things like snowflakes, ice, and salt are also crystals. The atomic arrangement of all crystals is orderly; the comprising atoms lock with each other in a specific way. The pattern gets repeated again and again when given the ideal controlled conditions to grow and until the materials last. The crystals we find in nature are called minerals and are unlike the perfect specimens displayed in natural museums. In nature, there are variations in temperature, pressure, invasion of impurities, and other conditions on earth that result in some anomalies, and lead to variation in the structure and arrangement of crystals. When various types of minerals grow near each other, they invade space and become a conglomerated mass. This phenomenon is common in the growth of crystalline rocks like granite. When impurities enter during crystal growth, they can impart different colors to the mineral. For example, pure quartz crystals are transparent or colorless, but impurities from the earth, like titanium, manganese, iron, etc., can give it many different colors. Amethyst, agate, onyx, and tiger’s eye, for example, are all quartz crystals colored by impurities.The characteristic symmetry of a single mineral is sometimes apparent to the naked eye as it gets reflected on flat surfaces of the crystal. However, if the crystal is very minute, like an ice crystal, it is necessary to check it with a magnifying glass or microscope. With experience, one can identify the symmetrical patterns in minerals and will be able to identify a specimen. However, some crystals may not have an apparent symmetry or may have some defects in their structure. If so, one will need an expert in crystallography or scientists from the field to help to classify them.In the world we live in today, scientists use crystals in things we use every day. Do you know LCDs, watches, microprocessors, and fiber optic communication lines, all use crystals in some form? Crystals are fascinating things, and the more you understand their structure, the more you will be able to appreciate their subtle beauty.In this article, we will read some interesting facts about crystals and learn how they form. If you find this piece interesting, you can also read our posts here on Kidadl how big was titanic? And how many legs do butterflies have?How are crystals formed?Crystals are termed growing, even though they are non-living. They start small but continue to expand as more atoms come together and repeat the crystal structure. The process through which crystals are formed is known as crystallization. Crystal formation is influenced by various factors, including pressure and temperature, and results in a beautiful array of crystals.The variety and symmetry of patterns in crystals have long drawn scientists to study them and have given rise to a specific branch of science for studying crystals called crystallography. In natural settings, when some liquids cool and start to solidify, crystals start forming. Some molecules come together in an attempt to become stable and reach stability by forming uniform, repeating patterns. The process of crystal formation can take a few days in some cases, to hundreds of years in natural settings. The crystals formed naturally deep inside the earth took perhaps a million years. When liquid rock, known as magma, cools down slowly, crystals are created. Precious gems like emeralds and rubies are formed this way in nature. Another method of crystal formation is evaporation. For example, when water evaporates from a saline mixture, salt crystals are formed.There are many different ways through which crystalline substances grow. They can be categorized into three primary methods, namely, crystal formation from vapor, from solution, and melt. The first example of crystal formation from vapor is ice crystal and snowflakes. For crystals to grow from vapor, the gas molecules must stick to a surface and form the crystal structure. Many conditions must be ideal for this to happen. Firstly, the solid-gas composition must be in a supersaturated state, which is a state of nonequilibrium where the number of gaseous molecules exceeds the solid molecules. The gaseous molecules leave the gas and will attach themselves to the container’s surface, and their growth happens there, layer by layer.One of the primary, critical stages in the process of crystal growth is seeding. To implement the seeding technique, a tiny crystal (referred to as the seed) of the desired shape is introduced in the container. The seed offers nucleation sites to the gaseous molecules for crystallization, and thus they grow gradually, one molecule at a time. To minimize any defects in the crystals, the temperature maintained is well below the melting point. This process by which crystals grow is slow, and it takes several days for a small crystal to form. However, the quality of crystals that grow this way is very high.Growing crystals from solution is similar to the process of forming crystals from vapor. However, here in the supersaturated mixture, the gas is replaced by the liquid. Through this method, large single crystals can be produced. DIY science projects for kids with salt and sugar are simple examples of solution-based crystal formation. The solvent used in this technique to immerse the seed crystal must consist of 10-30% of the needed solute. The pH and temperature of the solution must be controlled optimally for crystal growth. This method through which crystals grow is also relatively slow but is faster than when compared with the vapor technique. This is because the liquid is more concentrated than gas. The quality of crystals that grow this way is also quite good.The technique of growing crystals from melts is the most basic. In this method, a gas is first cooled to its liquid state, and then it is chilled to solidify. This method is a great way to create polycrystals; however, large single crystals can also be produced using special techniques like crystal pulling. Maintaining and controlling the temperature carefully is crucial for this method of crystallization.What are crystals?What do you visualize when you hear the word crystal? Beautiful gems and stones, crystalline things with smooth surfaces and symmetrical geometric shapes? As per science, the definition of crystals doesn’t come from outward appearance, it goes deep down into the atomic arrangement.A crystal is defined as a solid, with a precise, periodic, and ordered internal arrangement of atoms. The periodic pattern extends in all directions and forms the crystal lattice. The patterns in crystals are referred to as crystal systems. We use or come across many crystals in our day-to-day lives, like salt, ice crystal, sugar, snowflakes, graphite, and gems. Salt forms cubic crystals, whereas snowflakes have a hexagonal crystal. Table salt comprises sodium and chlorine ions. Each sodium ion is bound by six chloride ions, and each chloride ion is also bound by six sodium ions. This pattern is repeated throughout the salt crystal structure. Snowflakes comprise water molecules and form hexagonal plane crystals. Crystals with their periodic atomic patterns, smooth surface, and various shapes are a natural geological marvel on earth. Many people believe that crystals like quartz, amethyst, etc., have healing properties. Quartz is considered the master healing crystal and is used as a part of many spiritual rituals.The significance of the crystal structure is as vital as the atoms that comprise it. Do you know that both diamond and graphite are crystals made up of carbon? Yet, diamonds and graphite have totally different characteristics. Diamond is transparent, and is so strong that they are capable of cutting glass; on the other hand, graphite is opaque, dark, and so soft that it gets eroded when you rub it on paper. How are these two crystals made up of the same atoms of carbon so different? The answer lies in their crystal structure. In diamonds, the carbon atoms are bonded tightly in a packed structure. Every carbon atom is bound to four carbon atoms in the strongest three-dimensional bond ever, and this pattern is repeated, whereas, in graphite, the carbon atoms form layers one above the other. Diamonds grow deep within the earth’s crust when the carbon atoms are subjected to very high pressure, causing the atoms to bond in the highest crystalline structure possible.Properties Of CrystalsThe properties of crystals vary across their range. The properties of crystals can be anisotropic, which means that their properties can vary when tested from different axes or directions. The physical properties of crystals are vital because they determine their use in various areas.Some crystals have unique mechanical, electrical, and optical properties, making them especially useful in a particular industry. Hardness, heat conductivity, cleavage, electric conductivity, and optical properties are some of the physical properties of crystals that are checked to determine their usage. The hardness of the crystal is measured on the Mohs scale and can be defined as the resistance of a crystal to indentation or scratching. Diamond is the hardest mineral known and finds many industrial uses because of this property. Cleavage in minerals and crystals is its tendency to split along some structural lines or crystallographic planes. Knowing the cleavage helps in determining the planes of the weakness of the crystal.Crystals like Rochelle salt and quartz, have specific electrical properties like the piezoelectric effect. Due to this property, when the crystal is applied with some mechanical stress, an electric charge accumulates in it, making them suitable for use in communication equipment. Crystals like germanium, galena, silicon carbide, and silicon, carry current unevenly in various crystallographic directions and hence find usage as semiconductor rectifiers.Types Of CrystalsWhen you think of crystals or crystalline substances, you might think of various crystals like quartz, amethyst, jasper, or turquoise.Crystallography classifies crystals according to the type of chemical bonding that takes place between the constituent atoms; they are also classified according to the crystal structure. Let’s learn about the four basic types of crystals according to the chemical bond. They are called covalent, metallic, ionic, and molecular crystals.As the name suggests, covalent crystals are the crystals in which the atoms in the crystal are bound with covalent bonds. The network of these bonds is three-dimensional. Covalent bonds are very strong and the electrons are shared between atoms to create them. Crystals with covalent bonds are very hard. Examples of crystals with covalent bonds are diamond and quartz. Diamonds have a hardness of ten and quartz, seven on the Mohs hardness scale. Since a covalent crystal comprises atoms and no ions, it is not a good conductor of electricity in any form.In ionic crystals, the crystal structure grows by ionic bonds of positively and negatively charged ions. One example of an ionic crystal is salt. The melting point of ionic crystals is very high, and they are tough and brittle. In their solid-state, they do not conduct electricity. However, in the aqueous or molten state, they are a good conductor of electricity.Metallic crystals, as the name says, are made of metals and are held by metallic bonds. Examples of metallic crystals are copper, aluminum, and gold. They are shiny in appearance and have a wide range of melting points. Metallic crystal bonds have many mobile valence electrons, also known as delocalized electrons, which makes these crystals an excellent conductor of electricity.The molecular crystals are the weakest of all types of crystals. They are held together by not-so-strong intermolecular forces. Ice is an example of a molecular crystal that is bound together by hydrogen bonds. They have a low melting point and a low boiling point. Rock candy in your pantry is also a type of molecular crystal. Since they lack ions and free electrons, they are poor conductors of electricity.Another way of classifying crystals is based on the crystal structure. At an atomic level, crystals repeat a specific pattern, which determines the shape of the crystal. There are seven types of crystal structures, namely cubic, tetragonal, hexagonal, monoclinic, triclinic, trigonal, and orthorhombic. Crystal structures are also known as lattices.A cubic crystal structure is also known as isometric and has a simple cube shape. Octahedrons are also included in this crystal lattice type. Diamonds, silver, gold, fluorite, etc., exhibit this crystal structure. A tetragonal crystal structure is rectangular and also comprises double pyramids and prisms. Zircon, anatase, and rutile, for example, also have this structure. In the hexagonal crystal structure, there are six sides, and the top and bottom are flat. Emerald and aquamarine are examples of this crystal structure. Ruby, quartz, amethyst, calcite, etc., have a trigonal crystal structure; this crystal structure has a three-fold axis. The orthorhombic structure can be described as a conjoined pyramid shape. Topaz exhibits this crystal structure. The monoclinic crystal structure is found in moonstone; the structure resembles a skewed tetragon. Triclinic crystals have abstract forms, and this structure is found in turquoise.Here at Kidadl, we have carefully created lots of interesting family-friendly facts for everyone to enjoy! If you liked our suggestions for how do crystals form? Then why not take a look at how do clouds float? Or how are mirrors made?
The origin of the word crystal lies in the Greek word ‘Krustallos,’ which means ice as well as rock crystal.
