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.
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