The gossan is composed primarily of goethite, quartz (Si[O.sub.2]), beudantite
(Pb[Fe.sub.3](As[O.sub.4]) (S[O.sub.4])[(OH).sub.6]), jarosite ((K,Na)[Fe.sub.3][(S[O.sub.4]).sub.2][(OH).sub.6]), plumbojarosite [(Pb[Fe.sub.6](S[O.sub.4]).sub.4][(OH).sub.12]), argentojarosite (Ag[Fe.sub.3][(S[O.sub.4]).sub.2][(OH).sub.6]), bindheimite ([Pb.sub.2][Sb.sub.2][O.sub.6] (O,OH)) and scorodite with accessory cinnabar (HgS), native Ag, Au, and cassiterite (Sn[O.sub.2]) (Boyle 1995).
Goodchild, of the Scottish Geological Survey, found wulfenite there in 1875 but the locality only really became of interest to collectors in the 1950s following the reporting of a suite of rare supergene minerals including bayldonite, duftite, beudantite
, carminite, lindgrenite and stolzite (the first authenticated British occurrence).
The crystals line cavities to a few centimeters across in earthy brown limonite, associated with microcrystals of anglesite, arsenian siderite and beudantite
. Some of the larger specimens with dense crystal pocket-linings are quite attractive.
One proved to be beudantite
, but the other could not be identified with any known species.
Vein Minerals Adamite Goethite Arsenopyrite Gold Austinite Hemimorphite Barite Malachite Beudantite
Mimetite Calcite Smithsonite Cerussite Sphalerite Chalcopyrite Plumbojarosite Chlorargyrite Pyrite Chrysocolla Rosasite Conichalcite Tetrahedrite Fluorite Willemite Galena Wulfenite ACKNOWLEDGMENTS
Other minerals not directly associated with calderonite are: wulfenite, mimetite, cerussite, beudantite
, adamite, hemimorphite, smithsonite, chalcophanite, silver, quartz and Ca-Fe carbonates.
Occurrence: Associated minerals are: beudantite
, cuprian adamite, conichalcite, wulfenite, quartz and chalcocite.
Even so, extremely rare species such as germanium-rich beudantite
, schneiderhohnite, stottite and scorodite, can be seen in the collection as well-crystallized, aesthetic specimens.
Other minerals in the dump material are: cobaltaustinite, scorodite, bariumpharmacosiderite, olivenite, conichalcite, erythrite, arsenjosiderite, mimetite, beudantite
, silver, bismuth, acanthite, galena, pyrite and skutterudite.
Several specimens of a germanium-rich beudantite
crystals to 1.5 cm, which are regarded as the finest in the world, have been found in old collections of Tsumeb, Namibia, minerals.