English: Celestite from Indiana, USA. (public display, Geology Department, Wittenberg University, Springfield, Ohio, USA)

A mineral is a naturally-occurring, solid, inorganic, crystalline substance having a fairly definite chemical composition and having fairly definite physical properties. At its simplest, a mineral is a naturally-occurring solid chemical. Currently, there are over 5700 named and described minerals - about 200 of them are common and about 20 of them are very common. Mineral classification is based on anion chemistry. Major categories of minerals are: elements, sulfides, oxides, halides, carbonates, sulfates, phosphates, and silicates.

The sulfate minerals all contain one or more sulfate anions (SO4-2).

Celestite (a.k.a. celestine) is a strontium sulfate mineral, SrSO4. Its name has the same etymology as "celestial", meaning "sky", in reference its bluish to pale bluish crystals. This mineral has a nonmetallic luster, a clearish to whitish to pale blue to bluish-gray color, a white streak, a hardness of 3 to 3.5, two cleavages, and is noticeably heavy for its size. It forms diagenetically and also occurs in low-temperature hydrothermal vein systems.

Locality: undisclosed/unrecorded site at or near the town of Mitchell (but probably a quarry on the northeastern side of town), southern Lawrence County southern Indiana, USA

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Photo gallery of celestite:

www.mindat.org/gallery.php?min=927