What is Celestite?
Celestite, also called celestine, is a delicate strontium sulfate best known for sky-blue tabular crystals and elegant geodes from sedimentary and evaporite environments.
Mineralogy and structure
Reference formula: SrSO4. Celestite is a sulfate mineral in the baryte–celestine series. Celestite is orthorhombic with the ideal formula SrSO4 and is the strontium analogue of baryte. Barium, calcium and other substitutions can occur, but the pale blue colour is not by itself diagnostic. The reference record uses orthorhombic symmetry. Typical hardness is 3–3.5 on the Mohs scale and specific gravity is approximately 3.96–3.98.
Colour, lustre and habit
Typical colours include colourless, pale blue, white, grey, brown. The usual tabular, prismatic, granular habit and vitreous, pearly lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Celestite forms in or is associated with sedimentary evaporites, cavities in carbonate rocks, hydrothermal veins and late-stage geodes. Important documented localities include Madagascar, Sicily, Spain, England, the United States and Mexico.
Why collectors want it
The finest celestite is sold through colour, transparency and crystal architecture: sky-blue plates lining a geode create a calm, architectural display, while a precise locality adds scientific and commercial confidence.
Collecting and care
Celestite is soft and brittle. Protect thin plates from impact, pressure and vibration; keep specimens dry and avoid acids, harsh cleaners and ultrasonic treatment.
