The Periodic Spiral assigns the color blue (cyan blue) to beryllium, carbon, neon, strontium, molybdenum, palladium, tin, and xenon. Cyanine, an organic (carbon-based) blue dye discovered in 1856, is the basis for the cyan pigment. "Neon blue" is a common descriptor for a cyan blue hue, despite the inconvenient fact that neon emits a characteristic reddish-orange glow while conducting electricity in sealed glass tube. Xenon, the second of the inert gases designated on the Spiral as blue, emits a characteristic blue glow when excited in this way. Celestite, a sulfate ore of strontium, is a favorite among mineral collectors for its beautiful sky blue (celestial) color. In the thiogallate family of phosphors, the cerium-doped strontium thiogallate (SrGa2S4:Ce) thin film is regarded as the most promising blue phosphor material. The mysterious and intensely colored complex called molybdenum blue, discovered by Scheele in 1778, is familiar to chemistry students studying qualitative analysis, who try to identify the chemical composition of unknown materials. Both palladium and tin have a bluish tinge.