Celestine is a mineral with a hardness of 4 out of 10 on the Mohs scale of mineral hardness [?]. These Orthorhomibicly structured gems are made of strontium sulfate, their full chemical compound being SrSO4.
Celestine appears as colorless, or pale blue, and is transparent to translucent, and has two directions of cleavage. It is very brittle, and has a vitreous to pearly luster.
It occurs in sediments associated with sulfur, with evaporate minerals like gypsum, anhydrite, and halite; in hydrothermal veins with galena and sphalerite; as concretions in clay and marl; in cavities in basic lavas, and in the cap-rock of salt domes.
It is insoluble in acids, but slightly soluble in water, and may fluoresce under ultraviolet light. When heated, it fuses easily, giving a milk-white globule, and colors the flame crimson.
Some visual examples are the bluish crystals in England, seen in gypsum and sulfur deposits in Italy, large crystals in the USA, pale-blue crystals in basalt cavities in Italy, and in pegmatites in Bohemia and Madagascar.
Celestine got its name from the Latin word for "celestial," after the beautiful pale color shown by some of its finest crystals. It is also known as celestite.
Celestine is the chief ore of strontium. Strontium and its salts are used in fireworks and flares to impart a strong crimson color. The crimson coloration of the flame is one of the tests used for identifying strontium salts.
It is also used in the nuclear industry, in the manufacture of rubber, paint and electrical batteries, in the refining of beet sugar and in the preparation of iridescent glass and porcelain. It is much sought-after by museums and collectors.
Ornamental-quality celestine is found in Bristol (England). Most faceted celestine comes from Madagascar (blue), or Canada (orange). Facetable crystals come from Tsumeb (Namibia).