What Are Crystals & How Are They Formed?

What Are Crystals?

• Crystals are solid matter made up of atoms, molecules or ions that are organized in a lattice structure. These structures are repeating patterns that occur in three dimensions and form via a process called crystallization. In total, there are 14 crystal lattice arrangements possible. Crystal structure and chemical composition are the defining characteristics of any given mineral. Even minerals with the same chemical composition are considered different If their lattice arrangement differs.

How Are Crystals Made?

• Crystallization is the natural process by which two events lead to the proliferation of crystalline phases. First the atoms or molecules precipitate out of a solution and begin to cluster together, forming stable nuclei. This event is appropriately named "nucleation". Following nucleation, crystal growth can occur as each nuclei reaches what is known as "critical size." Chemists often induce this process by using specific chemicals and temperatures to form crystals in the lab setting.

Chemical Properties of Crystals

• There are nine classes of crystalline minerals including the silicate, carbonate, sulfate, halide, oxide, sulfide, phosphate, element and organic classes. Carbonate minerals can be found in the ocean as a result of decaying plankton shells that accumulate on the sea floor. Sulfide, oxide and element classes can be found as metal ore and are important in the mining industry. Apatite is a phosphate mineral that is found in the teeth and bones of animals.

Physical Properties of Crystals

• Classifying crystals has a lot to do with the structure and hardness they exhibit. The elementary physical form of the crystal is known as the crystal "habit." Rock crystals and gems have good crystal habit, while sugars, nitrates and salt are granular and difficult to perceive as crystals at first. Other qualities that determine crystal identity are color and luster, or how light interacts with the surface of the mineral.