Chemical Composition: SrSO4
Mohs' Hardness: 3-3.5
Transparency: Transparent
specific gravity: 3.97-4.00

Celestite is one of the most beautiful gems I've seen, which is expected from a stone named after the latin word for the sky, caelum. Celestite can vary in color from a light sky blue to white, to even a greyish color. One specimen, pictured in Rocks and Minerals, looked like crystalized water. Not ice, but crystalized Caribbean ocean water, pure and sparkling. The pale blue color is attributed to minuscule amounts of gold trapped in the gem. It is no wonder that this mineral is prized by many museums and collectors.

Besides looking pretty, celestite is an important source of strontium. Strontium is used in making anything from rubber, paint, as part of the glass in computer monitors and television screens, military tracers, and fireworks. Because of the strontium, shavings of celestite will burn bright red. In fact, to test celestite against the similarly shaped light blue barite, shavings of the questionable crystal are to be burnt. The strontium will burn red, whereas the barium in barite burns with a green hue.

Celestite can be found in a few geologic formations. Rarely, it can be found in a vein, in matrices of galena, sphalerite or other sulfides. More often, it is found in the cavaties of volcanic rocks or as geodes or nodules in sedimentary rocks, usually the cavities of sandstone or limestone. Geographically, celestite can be found in Vicenza, Italy as well as the Malagasay Republic, Madagascar, Germany, Bristol, England, Ohio, Michigan, and New York, as well as other locations.

Gemstones of the World, by Walter Schumann. Sterling Publishing Co., New York, 1979
Simon and Schuster's guide to Rocks and Minerals, Simon and Schuster Inc. New York, 1978