Introduction: banalsite is a rare mineral which belongs to the feldspar family and may form a solid solution with stronalsite (Na₂SrAl₄Si₄O₁₆). It was the first barium aluminium silicate to be described with sodium as the dominant alkali. Banalsite forms under hydrothermal or metamorphic conditions. The name banalsite was formulated from its constituent chemical elements (Ba, Na, Al and Si).

Occurrence in Wales: banalsite was described as a new species by Campbell Smith et al. (1944a&b) from Benallt Mine during the Second World War, when the mine was re-opened by the Home Ore Department of Iron and Steel Control of the Ministry of Defence. It is only known in Wales from the type locality. Initially only massive material was described (Campbell Smith et al., 1944a&b) but later finds revealed crystalline material enabling crystallographic data to be published (Campbell Smith, 1945). Banalsite from the type locality is found in veins and vugs where it is associated with a suite of minerals believed to have been derived from hydrothermal activity involving manganese-rich fluids exhaled onto the Ordovician sea floor (Brown & Evans, 1989).

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