Barium feldspar and barian muscovite are major constituents of the Aberfeldy Ba-Zn mineralization. Celsian varies from equigranular to a platy habit in quartz-celsian rock and forms porphyroblasts in schist and marble. Hyalophane is less common. Barian muscovite is a major component of the schist in the mineralized zone. Celsian (> 80 % Cn) and/or hyalophane coexist with muscovite containing c.6% Ba, and c.8.5% Ba was measured in muscovite from one feldspar-free specimen. Cymrite separated from foliated quartz-celsian rock conformed to the formula BaAl₂Si₂O₈·H₂O. The rock textures reflect regional metamorphism, but it is believed that the barium silicates are ultimately authigenic in origin. The platy habit of much of the celsian may have been inherited from cymrite formed during the development of tectonic fabrics.