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Celestite Mineral Facts:

Chemical Formula: SrSO₄
It is also frequently known as celestine, and very commonly has a light blue tone to which it owes it's name.

Colors: Colorless or White when pure, sometimes faintly blue or red.

Hardness: 3.0 to 3.5

Density: 3.95 to 3.97

Cleavage: Perfect basal cleavage and an almost perfect parallel to 010.

Crystallography: Orthorhombic
Celestite is found in tabular prismatic crystals, in fibrous and sometimes in granular or globular masses.

Luster:. Vitreous, transparent to translucent.

Optics: (Refractive Index)  a = 1.6220; y = 1.6237

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Composition, Structure and Associated Minerals:
Celestite is found in bedded deposits or disseminated through limestone and sometimes in nests and lining cavities in such a rock. In these concentrated areas, it sometimes occurs as crystals lining geodes in the same types of rock. It is also at times found as a gangue in metallic mineral veins. In some instances it was deposited by hot waters, in others by cold waters, and in others it was concentrated by the leaching of strontium-bearing limestones by atmospheric water.

The mineral is commonly associated with calcite, dolomite, gypsum, halite, sulphur, etc. Celestite often contains small quantities of the isomorphous Ca and Ba compounds. The name is derived from the Greek word celestis in allusion to the faint blue color often present.

Identification and Diagnostics
Before the blowpipe celestite reacts like barite except that it tinges the flame crimson. This crimson color may be obtained more distinctly
by fusing a little powder of the mineral on charcoal in the reducing flame and dissolving the resulting mass in a small quantity of hydrochloric acid, then adding some alcohol and igniting the mixture. It closely resembles barite and it will usually need a flame test (for strontium or barium) to positively differentiate the two species.

Occurrence, Localities and Origins:
Notable localities for its occurrence are with the sulphur deposits at Girgenti in Sicily; at Bex, Switzerland; Yate, Gloucestershire, England; Herrengrund, Hungary; in crystals and grains scattered through limestone, as at Strontian Island, Put-in-Bay, Lake Erie, Mineral County, West Virginia; San Bernardino County, California. Found disseminated in limestones near Syracuse, New York, and in Monroe
County, Michigan. Geode like nodules filled with light blue crystals make showy mineral specimens and are highly desired by collectors.

Although the mineral occurs in large quantities at a number of places in the United States and Canada, it is not commonly mined as there is only limited demand for the material. It is one of the chief ores of the metal strontium. A small quantity of the strontium oxide is annually imported. Strontium salts, prepared from celestite in part, are used in the preparation of nitrate of strontium for fireworks. Other strontium salts used in the refining of sugar. Strontium metal is used in some aluminum and magnesium alloys. Radioactive strontium 90 is used in the treatment of some cancers.  

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