Celestine: Gemstone Information
Celestine is strontium sulphate, SrSO4, and crystallizes in the orthorhombic system with tabular habit. The transparent crystals have two directions of cleavage and stones are faceted from colourless, yellowish or bluish green crystals. The hardness is 3.5. The SG is 3.97–4.00 and the RIs are 1.619, 1.623 and 1.631 biaxial positive with birefringence of 0.012. Gem quality material may have slightly higher values. A scraping taken from the girdle of a cut celestine may colour the Bunsen flame red. A whitish or bluish white glow is shown by celestine under UV.The origin of celestine is chiefly sedimentary. It occurs as cavity or fissure fillings, particularly in limestones and in hydrothermal veins.Ornamental-quality material is found at Yate, Bristol, England; most faceted celestine comes from Madagascar (blue) or Canada (orange).Facetable crystals from Tsumeb, Namibia.