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

As mentioned above

,twinning of plagioclase is very common. Frequency distribution of plagioclase feldspar twins is illustrated in Figure 3« The frequency of complex and parallel twins is 85%. The ratio of C-twins to A-twins is also great (C:A - 2:1). According to Gorai (1951)» A-twins are commonly present in the igneous as well as in the metamorphic rocks, while C-twins are confined to or are characteristic of the volcanic and plutonic rocks. Albite and acline twins belong to the former one, while the other twins belong to the latter one. Albite-ala has been found to be the most common twin law in the dike rocks. Mafic constituents. The dike rocks carry three kinds of mafic minerals, these are: hornblende, biotite, and diopsidic augite. The chief mafic mineral in the Sárhegy dike is hornblende, whereas the amount of hornblende and that of biotite is about the same in the Csala Forest dike, finally in the Székesfehérvár Quarry dike biotite is the only mafic mineral. A very small amount of diopsidic augite occurs in the Sárhegy and Csala Forest dike.It is associated with hornblende and biotite, or it is enclosed in these minerals. It has a rounded shape due to resorption. It is probable that diopsidic augite had crystallized before other mafic constituents, but reacting with the liquid phase volatile-bearing ferromagnesian minerals (hornblende, biotite) developed. Hornblende is present in two generations. Those belonging to the first generation form euhedral and subhedral phenocrysts of 1-3 mm size (Plate 3. Fig. 2.). Twinning on (100) is common at the larger crystals (Plate 3. Pig. l.).The pleochroism is fairly intense:t - dark brown, ß - pale brown, « = yellow. The extinction angle is generally small: (<p : C = 14-15°), but greater and smaller values were also recorded. In some cases the extinction angle is as small as 8°. The average value of optic