The Theory of Nothing

How do crystals form?

How do crystals form?

By crystals I mean a solid chemical structure whose atoms are arranged in a geometric pattern. Crystals start out in a microscopic form and grow to enormous sizes. However, for the most part crystals must be examined under a microscope.
Probably, the most valuable crystal is diamond, which is a lattice arrangement that is considered a metastable allotrope of carbon. What the heck does that mean? Carbon is an element that is found in many forms. Thus, an allotrope is a form of matter, and metastable means that it's not in its lowest stable state but can remain in the metastable state indefinitely.
Other allotropes of carbon are graphite and buckminsterfullerene (I've already discussed these).
Most chemists think of chemical salts as forming crystals. Familiar examples of these types of crystals are salt or sodium chloride, which forms cubic structured crystals, and Honey, which forms glucose crystals in a solution of fructose.
A good example of an inorganic crystal is sulfur, which is a bright yellow polyhedron crystalline solid. An example of an organic crystal is a favorite science project: rock candy, which is crystalized sucrose.
Natural crystallization occurs with minerals, such as the formation of stalactites and stalagmites of limestone in caves. Quartz is a natural crystalline form of silicon in the form of silicon dioxide that forms a six-sided prism. Most gems are crystals, such as Amethyst, Opal, Ruby, Emerald, etc. Natural processes that require heat and pressure over long periods of time form many of these crystals, such as diamonds and quartz.
Snowflakes are considered a crystal of water. Actually, a snowflake is an aggregation form of ice crystals that can assume various forms. Snowflakes always assemble in a six-sided structures but the variation in the pedals is almost unlimited. Ice crystals form from seeds in the atmosphere and grow into intricate snowflake forms before coming down on us.
But, what makes crystals form? This is a good question and it is best answered by considering the chemical structure of the crystal. Salt is an ionic crystal and it's hard but often brittle. Salt crystals form with positively charged sodium ions attracted to negatively charged chlorine ions. These are very strong attractions and make a salt crystal hard.
Polar (have positive and negative charged ends) molecules, such as organic chemicals, form crystals because of van-der Walls force. This is a force that is caused by dipole attraction. It seems that a molecule's charge can be distributed in such a way as to make one end of the molecule more positive or more negative than the other side. Thus, the molecules can line up with the positively charged ends attracting and latching onto the negative charged ends.
Water molecules are dipolar and attract one another. When cooled, these dipolar forces cause the formation of crystalline structures, either ice cubes or snowflakes, depending on the circumstances.
Forced crystallization involves one of two methods. The first is a slow cooling process from a liquefied (melted) material. Sugar is a good example of this. The other method involves allowing a concentrated water solution to cool with evaporation. This often requires a seed crystal to promote crystallization. Chemists talk about recrystallization as means of purification. The other main chemical purification method is distillation.
Basically, crystallization is a physical process that causes molecules or atoms to form geometrically stable structures that we call crystals.

Thanks for reading.