Paragonite from the Dalradian

Abstract

TWO muscovite-rich red phyllites, one of chemical composition (per cent): SiO₂ 59.6, TiO₂ 0.9, Al₂O₃ 18.1, Fe₂O₃ 3.4, FeO 4.6, MnO 0.1, MgO 3.4, CaO 0.2, Na₂O 0.9, K₂O 4.7, H₂O 3.4, P₂O₅ 0.2, CO₂ nil, total 99.5, carry a quartz–paragonite–muscovite–chlorite–hæmatite–rutile–apatite mineral assemblage. They come from the Dunoon phyllite, a low-grade horizon of the Dalradian, ½ and ¾ mile north along the coast from Dunoon, Argyllshire. This is the first recorded appearance of paragonite as a rock-forming mineral from the Scottish metamorphic rocks, and its appearance elsewhere in low-grade rocks without albite is considered likely.