J.S. Mason - Central Wales Orefield: Bornite, Covellite

Bornite (L) is a rare supergene sulphide in the Central Wales Orefield. Here, it forms a striking flamelike intergrowth with chalcopyrite, set in a matrix of "chalcocite", and is an intermediate product of chalcopyrite to chalcocite conversion. The sample is from Llechweddhelyg mine, one of a few mines in Central Wales where a deep, intense supergene alteration zone has been preserved. The aggregate is just over 100 microns across.
Covellite (blue, L) is much commoner than bornite, and occurs wherever the precursor - chalcopyrite - is present. Typically it just forms filmy coatings but in some cases the conversion to covellite is more intense. Here, only a small yellow chalcopyrite core remains. This sample is from Esgairhir mine, and is ca. 1mm across.