Let's learn about the #geology of #celestite
Celestite or #Celestine gets its name from the Latin word coelestis, meaning “heavenly”. It is a natural form of strontium, however, it has the ability to contain both strontium and barite in different amounts freely. Calcium can also be present but is less common. Celestite is one of these rare varieties and can be colorless, white, light red, green, blue, or brown. The most desirable color is light blue.
Celestite forms in the cracks of mainly sedimentary rocks like limestone and dolomites, but it can also form in hydrothermal deposits as well as an evaporite in a desert environment. The crystals are formed by groundwater that deposits the mineral into empty cavities in the host rock. When Celestite geodes form the replacement of alabaster nodules consisting of calcium sulfates (gypsum or anhydrides), strontium-bearing solutions come into contact with calcium sulfate nodules that then dissolve the calcium away. This is why Celestite is found immediately above or below gypsum or anhydrite deposits. After this happens, empty cavities are left behind. The strontium then immediately precipitates as Celestite with its crystal forming in the empty cavities left behind from the dissolved calcium.
The Celestite geodes are extracted from the mine by hand through narrow vertical shafts, and once they are brought to the surface, they are cracked open to reveal the crystals within. The blue color is delicate and can fade quickly if continually exposed to sunlight.
The celestite crystals are stunning but also very fragile. On the Mohs scale of mineral hardness Celestite grades from 3 to 3.5. This means that it can be scratched very easily, and is more commonly found in natural clusters, as cutting and polishing are made more difficult due to its softness.
The best specimens come from Madagascar and form large well-defined light-blue crystals growing inside geodes. Other deposits of celestite are found in Austria, Britain, Canada, Germany, Italy, Mexico, Slovakia, and the United States (California and Ohio).
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