Yttrium is a metallic chemical element which is often found in compounds with the rare earth metals. It occurs in nearly all of the rare-earth minerals. Analysis of lunar rock samples obtained during the Apollo missions show a relatively high yttrium content. Yttrium is one of four elements named for the same small town of Ytterby, Sweden. The other three elements are  erbium, terbium,  and  ytterbium.  The element was discovered in 1794 by Finnish chemist Johan Gadolin (1760-1852). The discovery of yttrium marked the beginning of one hundred years of complicated chemical research that resulted in the discovery often new elements. Yttrium was used in many applications. Principal uses were in phosphors used in color televisions and computer monitors, trichromatic fluorescent lights, temperature sensors, and X-ray intensifying screens. As a stabilizer in zirconia, yttrium was used in wear-resistant and corrosion-resistant cutting tools, seals and bearings, high-temperature refractories for continuous casting nozzles, jet engine coatings, oxygen sensors in automobile engines, and simulant gemstones.