Kaszab Zoltán (szerk.): A Magyar Természettudományi Múzeum évkönyve 65. (Budapest 1973)

Embey-Isztin, A.: On the problem of graphic intergrowth and normal granitic structure

where fringes of potash feldspar are surrounded, or almost surrounded, by granophyric quartz. Besides quartz-metasomatism other replacement processes also took place during the postmagmatic evolution of the aplitic microgranite. Thus sericitization, turmalinization and an interesting kind of replacement of if-feldspar by plagioclase are worth mentioning. The latter phenomenon is somewhat similar to that of albitization, as the plagioclase develops at the boundary of older minerals, especially at the boundary of plagioclase (older generation) and potash feldspar, as well as between two potash feldspars (Plate III, Fig. 1). The small crystals of plagioclase are often structurally parallel to the adjacent older plagioclase crystal on which they have grown. However, they penetrate the potash feldspar in some cases' forming a "plagioclase ring" within the crystal (Plate III, Fig. 2). The Fig. 2. Granophyric quartz positions showing three maxima. Dotted lines: fissures in quartz newly formed plagioclase crystals contain few quartz exsolutions (Plate III, Fig. 3), from which it can be deduced that their composition is not pure albite. As a matter of fact, they proved to have a composition of 27 An %, by the use of the universal stage method. Thus certain similarity to the oligoclase-mantled potash feldspar ovoids in rapakivis is recognizable. Wherever intergranular oligoclase and granophyric quartz occur together, the