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, occurin 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 . (F . W .