Celestite, also known as celestine, is a strontium sulfate mineral with the chemical formula SrSO₄. It typically occurs in pale blue, colorless, or white crystals, although it can also appear in yellow, gray, and red varieties. Celestite forms in sedimentary rocks and is often found in geodes or crystalline masses. It has a Mohs hardness of 3 to 3.5, making it relatively soft and suitable for decorative pieces and collectible specimens. Major sources of celestite include Mexico, the United States, Canada, and Germany.