Zinc sulfate is the zinc salt of sulfuric acid and one of the most important sources of the essential trace element zinc. It is usually produced as a white, crystalline powder that is readily soluble in water. It most commonly occurs as the heptahydrate, which is also known by the historical name white vitriol (or zinc vitriol). This salt decomposes upon strong heating, thereby losing its water content. Due to its properties, it is used in many fields as a bioavailable source of zinc. However, in high concentrations, zinc sulfate can have an irritating effect on mucous membranes.