Rocks of phonolitic composition l.s. are found in the Ribeira Valley area mainly as dikes and plugs associated with alkaline complexes or also as small dikes intruding into granitic rocks of the Três Córregos massif. These rocks have been described in Banhadão, Itapirapuã and Mato Preto complexes, in Barra do Teixeira, Barra do Ponta Grossa and Sete Quedas plugs and also as dikes in a few places such as Morro do Chapéu, Cerro Azul and along the road Sete Quedas-Dr. Ulisses (SQ-Dr. U). Petrographically, they are classified as peralkaline phonolites (the most common type), phonolites, trachyphonolites and phonolitic nephelinites. Main minerais include alkali feldspar (in general rich in K 20 and less commonly in Na20); clinopyroxenes, varyingin composition from calcic (diopside, hedembergite and augite) to sodic-calcic (aegirine-augite) and up to sodic (aegirine) types; and nepheline. In minor amount are found biotite (titanium-biotite or titaniferous biotite); titanian garnet (in phonolitic nephelinites and also in Banhadão peralkaline phonolites); amphiboles and opaques (Mato Preto phonolites). On the basis of mineral chemistry, the investigated rocks can be placed into two groups showing different degrees of evolution. More primitive rock-types are represented by phonolitic nephelinites and phonolites while more evolved ones correspond to trachyphonolites and mostly to peralkaline phonolites.
