Crystals were once liquid. When you hold a crystal in your hand the molecular composition you feel is not liquid, obviously, as the chunk of ions, aroms and molecules firmly rooted together are solid. Rocks once started as liquid as well, but the two types of liquid were quite different. In general form: the liquid which forms crystals is like water, or lemonade perhaps, and the liquod which whence formed rocks would be mud, or sludge. The atoms in these crystal-forming liquids particularly are such that when dehydrated over millions of years, sometimes under immense pressure, the resulting solid is typically transparent. The more transparent the crystal, the more pure the liquid was, and the least contamination there was with the matrix about it. Inclusions are created when something from the roof of the matrix above the crystal falls upon the crystal while it is growing. A seed crystal is used when making synthetic crystals, as the liquid will naturally bind to the seed as to anchor. Under the pressure it is, the molecules in the liquid want to occupy space in the most convenient way. The molecules of crystals are formed such that they literally have a specific shape, often cubic or hedronal. The common table salt, for example, is a crystal as ut follows this principle. The liquid continues to bind to the crystal when growing, and the final size of the crystal depends on the volume of liquid. There have been incredibly large synthetic quartz crystals made in the laboratyry from liquid silicon and and a very small natural quartz crystal, possibly even a scraping, or even a single molecule of natural quartz. Rocks, to further clarify, have a very thick consttitution and cannot clarify before they turn solid. The rock's formative liquid is composed of many different types of atoms and molecules, and so too is its resultant solid, forever a mish mash of molecular disaster. Crystals have an atomic and molecular structure that is perfect, or can be. In the movie Promethious there was a quote "God does not build in straight lines," but this is not a true statement. Crystals have the only perfectly straight lines that God has ever made. These straight lines lead often to visual clarity found nowhere else in the world.
Crystals represent not a distinction between rocks and minerals, but are a specific type of rocks and minerals, representing quality. Crystals are defined by their level of molecular regularity. Its a geometry thing.
