According to the Crystal Bible of Judy Hall, crystals formed with the creation of the Earth and continue to transform as the planet changes. Some were endured, others grew in flats deep below the earth, others lay in layers and others were created by drops.
Due to chemical impurities, radiation, Earth and Sun's emissions, and the exact way they form, each form of crystal has its own character. A crystal is created by a series of minerals and is characterized by its internal structure which can be identified by means of a microscope.
A large or small sample of the same type of crystal has exactly the same internal structure. This unique geometric matrix is the means by which crystals are recognized. Some have many different external shapes and colors at a level that may seem completely different from each other but because they have the same internal structure being classified under the same name. This structure is the critical point for the classification of crystals.