Mineral Species: Chalcosiderite and Dufrenite

Chemical Formula: CuFe+++6(PO4)4(OH)8·4(H2O)

Chemical Name: Copper Iron Phosphate Hydroxide

Mineral Class: Phosphate

Mineral Notes: Chalcosiderite is a rare copper phosphate mineral. It forms a solid solution series with Turquoise. Both have the same structure but slightly different chemistries. Turquoise is the aluminium end member whilst Chalcosiderite contains iron. The presence of iron gives Chalcosiderite a deeper blue-green colour than Turquoise. The colour is diagnostic for the species. 

Description: Rounded nodules of Chalcosiderite upon an iron-stained matrix. Many of these nodules are covered by brown Dufrenite. However, where the cover is incomplete, the deep blue-green of the Chalcosiderite shows through. The colour is very attractive and shows really well under a good light. The specimen comes from the well-known Mauer collection.

Location: Wheal Phoenix, Liskeard, Cornwall, England.