Celestine (mineral)
Celestine (the IMA-accepted name) or celestite is a mineral consisting of strontium sulfate (SrSO). The mineral is named for its occasional delicate blue color. Celestine and the carbonate mineral strontianite are the principal sources of the element strontium, commonly used in fireworks and in various metal alloys. Etymology. Celestine derives its name from the Latin word "caelestis" meaning celestial which in turn is derived from the Latin word "caelum" meaning sky or heaven. Occurrence. Celestine occurs as crystals, and also in compact massive and fibrous forms. It is mostly found in sedimentary rocks, often associated with the  minerals gypsum, anhydrite, and halite. The mineral is found worldwide, usually in small quantities. Pale blue crystal specimens are found in Madagascar. White and orange variants also occurred at Yate, Bristol, UK, where it was extracted for commercial purposes until the mid-20th century. The skeletons of the protozoan "Acantharea" are made of celestine, unlike those of other radiolarians which are made of silica. In carbonate marine sediments, burial dissolution is a recognised mechanism of celestine precipitation. It is sometimes used as a gemstone. Geodes. Celestine crystals are found in some geodes. The world's largest known geode, a celestine geode  in diameter at its widest point, is located near the village of Put-in-Bay, Ohio, on South Bass Island in Lake Erie. The geode has been converted into a viewing cave, Crystal Cave, with the crystals which once composed the floor of the geode removed. The geode has celestine crystals as wide as across, estimated to weigh up to each. Celestine geodes are understood to form by replacement of alabaster nodules consisting of the calcium sulfates gypsum or anhydrite. Calcium sulfate is sparingly soluble, but strontium sulfate is mostly insoluble. Strontium-bearing solutions that come into contact with calcium  sulfate nodules dissolve the calcium away, leaving a cavity. The strontium is immediately precipitated as celestine, with the crystals growing into the newly-formed cavity.