Celestine or celestite (SrSO4) is a mineral consisting of strontium sulfate. The mineral is named for its occasional delicate blue color. Celestine occurs as crystals, and also in compact massive and fibrous forms. It is mostly found in sedimentary rocks, often associated with the minerals anhydrite, and halite.
The mineral is found worldwide, usually in small quantities. The bodies of 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.