Dr. Nagy I. Zoltán szerk.: Fragmenta Mineralogica Et Palaentologica 3. 1972. (Budapest, 1972)

Minerals composing the dike rocks Quartz

. A part of the quartz may be present as xenoliths, but the main part certainly not. It was the last one to crystallize and it is xenomorphic. In the rock of the Sárhegy dike quartz occupies the angular interstices between hornblende and plagioclase crystals. Orthoclase was formed at a late stage, and it may either be xenomorphic or hypidiomorphic. In the Sárhegy dike intergranular orthoclase is also common. In the large orthoclase crystals of the Székesfehérvár Quarry dike, there are many biotite and plagioclase inclusions in random orientation. Orthoclase is either fine-perthitic or perthite-free (Plate 2. Pig. 4.). In some cases it has a turbid aspect, otherwise its crystals are transparent. It is important to emphasise that the crystals are untwinned almost without exeption, whereas twinning of orthoclase is common in the Velence granite. The 2V^ values vary between 33° and 75° but the average 2V

x values of orthoclase crystals originating from the three dike rocks are the same, 2V^. = 52° respectively. The average 2V^. value of fine-perthitic

, hypidiomorphic orthoclase crystals is 55°, while that of xenomorphic, perthite-free ones is 47°. Consequently the crystals that began to crystallize fomerly, have a greater degree of Al/Si distribution than those that developed at a later stage. The latter ones crystallized only after having injected between wall rocks, whereas the former ones began to develop before the emplacement. The frequency distribution of orthoclase 2V values is demonstrated in Figure 2. It X shows two maxima with a slight minimum between them. The two maxima (45-50° and 55-60°) correspond with the average 2V

x values of the two types of orthoclase above mentioned. On the basis of 2V values partly "intermediate orthoclase" structure X CM