Chalcosiderite is a rare mineral, a member of the Turquoise Group and is isostructural with turquoise. This fine, old-time specimen is from the West Phoenix Mine in Cornwall, the Type Locality for chalcosiderite. The vuggy front of the 3-dimensional, quartz-rich gossan matrix is richly lined with gemmy, forest-green, grape-like clusters of radial chalcosiderite blades on botryoidal goethite. The little quartz vein dividing the vug is a nice accent. This is excellent material from this historic Cornwall mine and is likely to be over 100 years old.