Bayldonite, (after Mimetite)

Size: 50 mm
Owner: Mariusz Oleszczuk
Photographer: Mariusz Oleszczuk

A rich example of bayldonite (XRD confirmed) pseudomorphing mimetite, with individual replacements to about 7 mm in length, and typically 1-2 mm in diameter. Similar specimens were common in the upper levels of the first oxidation zone but many of them, on analysis, turn out to be arsentsumebite after mimetite.  In this specimen, however, the replacing mineral is bayldonite, and arsentsumebite was not detected in the analysis.

A closer view (Photograph 2; FOV 25 mm) reveals that many of the replacements are, in fact hollow epimorphs, and that the walls of these structures show a distinct concentric colour zoning.  Furthermore, tiny (sub-mm) isolated tablets of colourless to pale-tan wulfenite crystals are scattered liberally over the specimen, nestling in the interstices between the epimorphs.