A rare secondary Cu-Zn mineral occurring in the oxidised zones of base metal deposits. Containing both zinc and copper (with the latter responsible for its rich blue to emerald green hues) we have a rare phosphate that forms when primary deposits of ore sulphides are replaced by secondary minerals due to the action of waters that have been oxygenated and mineralised close to the surface as erosion slowly uncovers the deposit. It is too soft for jewellery use, being but 3.5 on Mohs scale, though the odd piece has been faceted for collectors. Prices are usually high, especially for larger prism or wedge shaped crystals as the most usual form is as a light dusting or granular crust on other minerals.
Colour: Green, blue, greenish ...
Hardness: 3½ - 4