Quartz, SiO2. Bryn Y Rafr mine, west Wales. Common in hydrothermal ore deposits, brecciated rock is produced by means of hydraulic brecciation. The walls of host rock within fissures is fractured because of changing pressures in hot circulating mineral rich fluids, and is mixed with minerals precipitating from the fluids as it cools,in this instance quartz.
Quartz, SiO2, Dyife mine Nr Staylittle,Central Wales Orefield. Miscellaneous specimens of brecciated material, with small quartz crystals and druzy quartz filling the crevices. Collected for simply being"pretty" specimens.
Calcite, Calcium carbonate, CaCO3. Nantiago mine, Central Wales Orefield. Calcite displaying typical rhomboid form and cleavage. An abundance of this gangue mineral is to be found at the mine.
Marcasite,FeS2, and Quartz,SiO2. Bryn y Rafr mine, west Wales. Country rock with quartz and marcasite content. The marcasite has suffered from "pyrite decay", breaking down into sulphuric acid and hydrous iron sulphate, the light coloured deposit on the surface.
Baryte,Barium sulphate, BaSO4, Gorn mine, Nr. Llanidloes, Central Wales Orefield. Massive baryte with "cockscomb" crystals on the surface.