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

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

Fig. 3. Frequency distribution of 200 xenomorphic quartz grains, Aplitic microgranite latter cuts the former (Plate III, Fig. 4). Hence granophyric quartz must be younger and as it cuts all the previous minerals and structural elements, it must have originated through postmagmatic, metasomatic processes. Orientation of quartz optical axes DRESCHER-KADEN (1948) pointed out that the so-called FERSMANN rule for graphic granites (the c-axis of quartz hes on a minor circle of 42° 15' around the c-axis of feldspar) cannot be generalised. However, the influence of feldspar,on the structural orientation of graphic-granophyric quartz is undeniable. In accordance with this, we found that the maxima of the c-axes of graphic quartz he either on the minor circle of 42°, or on a circle of about 60-64°, or somewhere else (Figs. 1-2). As it was already mentioned, transitions from granophyric to xenomorphic quartz of normal granitic structure are often met with in the aplitic microgranite. From this it can be deduced that no significant difference can exist in their genesis (DRESCHER-KADEN 1948). In order to obtain more evidence for this we have measured the relative positions of the c-axes of xenomorphic quartz grains to the c-axes of adjacent potash feldspar crystals and plotted them in frequency diagrams