- Blue Copper 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 (CuSO4·5H2O), the most commonly encountered salt, is bright blue
- The anhydrous form occurs as a rare mineral known as chalcocyanite
- The hydrated Blue Copper occurs in nature as chalcanthite (pentahydrate) and two more rare ones: bonattite (trihydrate) and boothite (heptahydrate). Archaic names for copper(II) sulfate are "blue vitriol" and "bluestone"