When ground water carrying dissolved silica is forced into a porous area of the rock, rapid cooling often occurs, causing the formation of tiny crystals on the surfaces or in cavities of the rock. The clear crystals often form on top of previously deposited minerals and gives druzy its unique look.  Many different types of minerals form druzy.  Chrysocholla, pyrite, carnelian, amethyst are all gemstones that have druzy variations.  Druzy is a natural stone, and will vary in shape, size & color from piece to piece.