The banded structure which these rocks commonly present in the field is only in a small measure due to plastic deformation, but is to a large extent original, and has been produced by flow in a viscous crystallizing intrusive magma, together with differentiation or segregation of the mass into bands of different chemical and mineralogical composition.
A estrutura bandeada que presentan comunmente estas rochas no campo é só nunha pequena medida debida á deformación plástica, xa que en gran medida é orixinal e foi producida polo fluxo nun magma intrusivo viscoso en cristalización, xunto coa diferenciación ou segregación da masa en bandas de diferente composición química e mineralóxica.