Ankerite, Calcium,iron,magnesium,manganese,carbonate, Ca(Fe,Mg,Mn)(CO3)2. Eaglebrook mine, west Wales. Although I have listed this specimen as ankerite, it may well be Ferroan dolomite. Both of these minerals have been recorded at this mine. The true identity can only be discovered by analytical means.The exposed rhomohedral fracture surfaces have a slight curvature, and the colour varies in shades of brown across the specimen.
Marcasite FeS2, and Quartz, SiO2. Bryn y Rafr mine, west Wales. Alternating layers of marcasite and quartz. The marcasite is subject to pyrite decay, hence the yellow sulphurous deposits. The quartz shows very little evidence of crystals, instead it appears as though it has flowed over the marcasite.
Calcite, CaCO3, and Quartz, SiO2. Nantiera mine, Central Wales Orefield. The specimens are predominately calcite in the form of platy crystals. Some of the calcite has been overlain with well defined stubby prismatic crystals of quartz, implying that there have been at least two episodes of mineral deposition at the mine.
Galena, PbS, and Quartz, SiO2. Nantiera mine, Central Wales Orefield. Broken galena crystals in a bed of druzy quartz, deposited in a fractured host rock. There are also minor amounts of chalcopyrite.
Brochantite, a cupric sulphate mineral,Cu4SO4(OH)6. Geufron mine, Central Wales Orefield. This sulphate mineral is a secondary mineral of copper, which along with lead was a product of the mine. The specimens were recovered from the spoil heaps at the mine, and are random growths of very small crystalline brochantite embedded in loosely cemented debris.