Celestine, or Celestite, a name applied to native strontium sulphate (SrSO4), having been suggested by the celestial blue colour which it occasionally presents. This colour has been referred to a trace of iron phosphate, but in some cases such an explanation appears doubtful. The mineral is usually colourless, or has only a delicate shade of blue. Celestine crystallizes in the orthorhombic system, being isomorphous with barytes (q.v.). The angle between the prism faces is 76° 17′. The cleavage is perfect parallel to the basal pinacoid, and less marked parallel to the prism. Although celestine much resembles barytes in its physical properties, having for example the same degree of hardness (3), it is less dense, its specific gravity being 3.9. Celestine is a less abundant mineral than barytes. It is, however, much more soluble, and occurs frequently in mineral waters. W.W. Stoddart showed that many plants growing on Keuper marls containing celestine near Bristol appropriated the strontium salt, and the metal could be detected spectroscopically in their ashes.
Celestine occurs in the Triassic rocks of Britain, especially in veins and geodes in the Keuper marl in the neighbourhood of Bristol. At Wickwar and Yate in Gloucestershire it is worked for industrial purposes. Colourless crystals, of great beauty, occur in association with calcite and native sulphur in the sulphur deposits of Sicily, as at Girgenti. Fine blue crystals are yielded by the copper mines of Herrengrund, in Hungary; a dark blue fibrous form is known from Jena; and small crystals occur in flint at Meudon near Paris. Very large tabular crystals are found in limestone on Strontian Island in Lake Erie; and a blue fibrous variety from near Frankstown, Blair Co., Penn., is notable as having been the original celestine on which the species was founded by A.G. Werner in 1798.
Celestine is much used for the preparation of strontium hydrate, which is employed in refining beetroot sugar in Germany. The mineral is used also as a source of various salts of strontium such as the nitrate, which finds application in pyrotechny for the production of red fire.
