Opal: Opal is a Hydrated (water inside) form of Silica. Opal can have a play of color inside, or it can be completely opaque. Opaque opals such as colored opals like Pink, Blue, and Tiffany Stone (purple) have other minerals or elements trapped inside them. Tiffany Stone, for example, has Fluorite making it purple, and Beryllium (a nonferrous metal) making it heavy. However, most opals appear very light for their size, and many, although not all, require stabilization of some type in order to cut and polish. The word Opal was derived from the Greek word "Opallios" meaning "to see a change of color", however, very few opals actually show a change of color. Most opals are either colored opal, opalized organic material, or common opal (white opal).