Dendrites in quartz are a kind of secondary inclusion. Dendrites filled a fracture in the solid quartz, instead to be included in the quartz during crystal growth as most of the inclusions. The rough is a massive quartz with intricate fracture pattern that make quite difficult to obtain the right cut. Some stones can be very big, but the quality of the quartz in big stones is usually low.
Dendrites in quartz are quite common worldwide, but material with the quality for cut gemstones are found only in Minas Gerais, Brazil.