Celestine is a mineral, strontium sulfate (SrSO4),
with distinctive pale blue or white, glassy, orthorhombic crystals, sometimes
occurring in fibrous masses. It is found chiefly in sedimentary rock and also as gangue material in ore veins.
There are deposits in Britain, Sicily, and the USA. It is an important source
of strontium and its compounds.
AND PLANETARY SCIENCE