On the origin of graphic granite Available to Purchase

For over a century, the origin of the quartz-feldspar intergrowth known as graphic granite has been debated in the literature. These textures have been produced experimentally during a study of the phase equilibria and nucleation and growth characteristics of granitic pegmatites. Analysis of temperature, pressure, and compositional variables suggests that the texture is produced by the simultaneous growth of quartz and feldspar in a kinetically driven, nonequilibrium situation. The growing interface of the host phase, a sodic alkali feldspar, is degraded from planar to cellular by the development of a SiO₂- (and probably H₂O-) enriched boundary layer. Between the cell boundaries, the SiO₂ content of the residual liquid achieves a level of supersaturation that allows quartz to nucleate and grow along with the feldspar. The bulk composition may well be on a cotectic surface, but under this mechanism it is not necessary. The development of this texture is dependent upon local kinetics at the interface rather than being solely tied to the thermochemical equilibrium of the bulk composition.