Zinc Sulphate Heptahydrate is an inorganic compound and can be offered in two different grades, the other being Zinc Sulphate Monohydrate. It is freely soluble in water. Zinc is naturally found in the Earth’s crust and is an inherent part of our environment. It is present in rock, soil, air, water, and the biosphere, and is also found in the bodies of plants, animals, and humans. The average natural level of zinc in the Earth’s crust is 70 mg/kg (dry weight), ranging from 10 to 300 mg/kg. Centuries ago, zinc ores were used for making brass and zinc compounds, as well as for healing wounds.