Copper(II) sulfate is the chemical compound with the formula CuSO4. This salt exists as a series of compounds that differ in their degree of hydration. The anhydrous form is a pale green or gray-white powder, whereas the pentahydrate, the most commonly encountered salt, is bright blue. It is used as a blue flame colorant in ammonium perchlorate based compositions where it sometimes substitutes the more expensive Paris green. The resulting blue color is almost as good as with the latter. It is not easily scattered and not anywhere near as toxic. Small amounts of copper sulfate are contained even in mineral waters. Copper sulfate can be used as a minor oxidizer and in combination with finely powdered Mg can be used as a pressure sensitive composition due to the waters of hydration (this is very unstable though). Copper sulfate is not good for colored flash experimentation,though.