The mineral celestite or Celestien or Celestine is a strontium-sulfate, and has the chemical formula SrSO4. Celestien comes both as separate crystals as in compact massive and fibrous forms. The hardness is 3 and the average density is 3.95. It is not radioactive. The mineral is named after the Latin word caelestinus, which means “heavenly”. It is mainly found in sedimentary rocks, and in evaporites where together with the mineral gypsum, anhydrite and halite. The mineral is found throughout the world, usually in small quantities. Weak blue crystals found in the Sakoany Mine, Vallée de la Sofia, Mahajanga Province in Madagascar.