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Celestite, also referred to as celestine, is a strontium sulfate mineral found in the 1790s. It is found within sedimentary environments, rarely in metal ore veins, and is isomorphous with barite (and may partially replace it), although barite is a bit heavier. Celestite is named after the latin term caelestis, meaning “celestial”, or “heavenly”, alluding to its sky blue color. Celestite is found in well-shaped crystals with the majority of its color displayed in a wide range of blues, however it can also present itself as specimens of white, yellow, light orange to reddish-brown, colorless, and pale green. While pure celestite is colorless, various impurities give this mineral its wide range of colors. It is very soft, rating a 3-3.5 on the Mohs scale, and for this reason it is often only seen in mineral collections and not used as gemstones in jewelry. Celestite is the main source of the element strontium, which is used in various metal alloys in the manufacture of pyrotechnics, flares, and fireworks due to its brilliant red flame when heated. This special characteristic is called thermoluminescence. Celestite also occasionally fluoresces under short wave ultraviolet light. These characteristics make celestite heat and light sensitive. Notable, large blue celestite crystals are found in Madagascar, often in enormous geode form. Italy, Spain, USA (Ohio, Pennsylvania), Poland, Libya, South Africa and Turkmenistan are other important locales where celestite is sourced.