Blue miracle or blue poison?
Would you have guessed that this copper sulphate stage in the colors of Chemnitz (or alternatively the Ukraine or Sweden) is a breeding?
The mineral with the chemical formula CuSO4 is only known in nature from around twenty sites. It is formed during the weathering of sulphide copper ores and is only stable in very dry areas due to its high water solubility. Copper sulphate usually occurs as a colorless, inconspicuous powder. In contrast, hydrates of the copper salt catch the eye due to the blue to turquoise color of the hydrous crystals. The most common form is copper sulphate pentahydrate or chalcanthite (Cu[SO4]-5H2O).
For centuries, copper sulphate was used in a variety of ways - as an emetic and wound healing agent in medicine, as a pesticide and stabilizer of chlorophyll in green vegetables in agriculture or for the production of copper-containing paints in manufacturing. Copper sulphate was also used to combat blue-green algae in swimming pools. However, as the substance is highly corrosive and hardly biodegradable, its use is declining in most areas. Occasionally, it is still used as a contrast agent in magnetic resonance spectroscopy (MRS) due to its paramagnetic properties, is used to etch copper engravings and provides bluish-green colors for New Year's Eve rockets. It is also still popular in school for experiments on crystal growth. But be careful - safety goggles, gloves and lab coats are essential for the experiments.
As copper has been named Mineral of the Year 2025, you will soon be able to admire other copper minerals in a highlight showcase at the Museum für Naturkunde alongside solid copper.