A white, chalky deposit of calcium carbonate found in kettles, washing machines etc., especially in a hard water area.
A bright green mineral, a basic copper carbonate, Cu₂CO₃(OH)₂; one of the principal ores of copper.
A mild green colour, like that of the mineral.
Of a colour ranging from olive-taupe to a mild to deeply-rich (at times seemingly translucent) green, like that of the mineral which is present on oxidized copper.