Abstract

Mineral phases and element localization were investigated in the vivid turquoise-coloured lichen, Lecanora polytropa, sampled from a psammite boulder in a wall supporting mine spoil at the abandoned copper mine, Riddarhyttan Kopparverke, southern Sweden. Normally pale yellowish (usnic acid), the lichen is turquoise coloured internally with bluish inclusions. X-ray mapping shows that Cu occurs on and within the lichen and does not coincide with P or S, suggesting that it is indeed associated with carbon or other elements not detected (or reported) using X-ray mapping. Scanning electron microscopy in back-scatter mode confirmed that the greatest Cu concentrations occur in the form of crystalline aggregates in coloured inclusions below the major internal turquoise layer with smaller Cu contents. X-ray diffraction with a position-sensitive detector (XRD-PSD) confirmed coloured crystalline aggregates consisted of the copper oxalate, moolooite. The study confirms the value of XRD-PSD as a non-destructive tool to characterize small (~50 μm) metal oxalate inclusions obtained from within lichen samples.

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