Chalcopyrite, Copper iron sulphide, CuFeS2. Dylife mine spoil heaps, Nr. Staylittle, Central Wales Orefield. Although labelled as chalcopyrite, there are also equal amounts of sphalerite and quartz. The chalcopyrite is intermixed with quartz, and varies in colour from gold to bronze. The sphalerite is massive, with just a few obvious crystals, and the quartz is a mass of intergrown crystals. There is also a thin layer of calcite on part of the surface.
Quartz, SiO2. Bryn y Rafr mine, west Wales. An example of net veining on a small scale. The host rock does seem to be composed of two slightly different rocks. The difference in composition would encourage net veining, which in this case is quartz veining. There is a small area of very fine druzy quartz on the surface.
Baryte, Barium sulphate, BaSO4. Bryntail mine, Central Wales Orefield. A solid mass of intergrown bladed crystals. Centrally, the crystals are larger, while those in the lower part are quite small, suggesting that there were different episodes of growth. The Bryntail mine is one of the few mines in central Wales which produced commercial amounts of baryte.
Sphalerite, Zinc sulphide, ZnS, Dylife mine,Central Wales Orefield. The sphalerite is massive,with no discernable individual crystals,and enclosing one or two shards of original host rock,indicating an earlier episode of hydraulic brecciation. Also in the specimens is an equal amount of quartz,which does have intergrown crystals,albeit not very well defined, which suggests that the quartz grew into cavities after the original brecciation. Also observed on the surface are a few small deposits of galena,and a vey small deposit of chalcopyrite.
Marcasite, FeS2, and Quartz, SiO2. Bryn y Rafr mine, west Wales. A layer of marcasite, sandwiched between two layers of badly defined druzy quartz, one layer with much smaller crystals. The marcasite has suffered pyrite decay, hence the sulphurous deposits on the surface. Although the specimen is kept in a sealed box with silica dessicants to halt the decay, a steel label, also in the box is very badly rusted by the chemical reaction.