Minerals (Category B)
Celestite is a favorite among mineral collectors. Its sky blue (or celestial) color is very pretty, and is unique in the mineral kingdom. Celestite also forms with other colorful minerals, making very nice combinations. Blue Celestite with bright yellow sulfur is one of the most famous colorful combinations of minerals.
Celestite has the same structure as Barite (BaSO4), and forms very similar crystals. The two may seem identical by ordinary methods, but a flame test can distinguish them. By scraping the dust of the crystals into a gas flame, the color of the flame will confirm the identity of the crystal. If the flame is a pale green, it is barite, but if the flame is red, it is celestite. The flame test works because the elements barium (Ba) and strontium (Sr) react with the flame and produce those colors. Normally barite is not blue, but many specimens of blue barite are often misidentified as celestite.