Inclusions are other minerals found inside quartz crystals. Some are lovely, others have mud in them, you can find many things captured by quartz. A geological explanation of occurences of quartz in the state of Arkansas. Although quartz has a unique structure, so do many other minerals. That in combination with the chemistry is what makes a mineral a mineral.
Crystals have a huge following of metaphysical advocates.
A primer on what it's all about. Scientists have learned how to grow their own crystals in the laboratory. Short article with photos. This is crystallography. You can learn the different ways crystals look.