Celestite

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Celestite (Sr S O₄) is a mineral consisting of strontium sulfate. The mineral is also known as celestine and is named for its occasional delicate blue color.

The International Mineralogical Association Commission on New Minerals and Mineral Names (CNMMN) has discredited Celestite as a valid mineral name. Celestine is the approved name for this mineral (see CNMMN report, p. 26).

Celestite occurs as crystals, and also in compact massive and fibrous forms. It is mostly found in sedimentary rocks, often associated with the minerals gypsum, anhydrite, and halite.

The mineral is found worldwide, usually in small quantities. Pale blue crystal specimens are found in Madagascar.

The bodies of Acantharea are made of celestite, unlike those of other radiolarians which are made of silica.

The largest known celestite geode is located near the village of Put-in-Bay, Ohio on South Bass Island in Lake Erie. The geode is 35 feet in diameter at its widest point. It has been converted into a viewing cave, and the crystals which once composed the floor of the geode have been removed. The Crystal Cave has celestite crystals as wide as 18 inches across and weighing up to an estimated 300 lb.

Characteristics:

Hardness: 3 - 3.5
Specific Gravity: 3.95 - 3.97
Cleavage: Perfect on one crystal face parallel to long axis (001), and nearly perfect on a second face (110).
Streak: white
Composition: SrSO4 (Strontium Sulphate); sometimes contains minor calcium and/or barium.
Crystal System: Orthorhombic