Chalcosiderite is a rare member of the Turquoise Group and is isostructural with Turquoise. This very fine, old-time specimen is from Cornwall, which has the the Type Locality for Chalcosiderite within the district. The vuggy front of the 3-dimensional, quartz-rich gossan matrix is richly lined with gemmy, forest-green, clusters of radial Chalcosiderite blades. Great luster, which is far more evident in person - the piece just glows a deep green. Basically, about two-thirds of the specimen is covered with Chalcosiderite, which is outstanding. This is excellent material from this historic Cornwall mine and is likely to be over 100 years old. It is a large and very rich, museum sized example from the location. Although a mine name has not survived on the old German label with it, we believe this to be from the Phoenix.