Rock Crystal is the name given to all clear colorless quartz. Pure quartz, traditionally called rock crystal (often called clear quartz), is colorless and transparent (clear) or translucent.
Rock crystal can have the colorless clarity of pure water, unlike ordinary window glass which is a pale green. Yet the most common flaws (internal fractures) result in veils and colorful refractions that lend beauty to an otherwise ordinary object.
The best rock crystal sources are in the famous Hot Springs area of Arkansas, USA; Cumberland, England; St. Gotthard, Switzerland; Brazil and Madagascar. Large individual crystals of quartz have been found in Brazil, the largest weighs over 44 tons.
The ideal crystal shape is a six-sided prism terminating with six-sided pyramids at each end. In nature quartz crystals are often twinned, distorted, or so intergrown with adjacent crystals of quartz or other minerals as to only show part of this shape, or to lack obvious crystal faces altogether and appear massive.
Rock crystal often has inclusions of other minerals and these inclusions sometimes produce popular varieties wanted by quartz collectors from all over the world.