Kaszab Zoltán (szerk.): A Magyar Természettudományi Múzeum évkönyve 66. (Budapest 1974)

Örkényi-Bondor, L.: The plagioclase crystals of the andesite agglomerate from the Csattogó Hill in Börzsöny Mountains (Hungary)

Fig. 8. The anortite content as a function of grain size. te. We were unable to observe correlation between the anortite content and the twin laws ; to find proper correlation far more measurements and greater differences in acidic values would be necessary. In the zones, which follow one after the other,' the y optical symmetry axes are relatively close, the a and ß optical symmetry axes are farther from each other. The drawn twin axis from the optical symmetry axes is always more precise with the least triangle of error at the Roc-Tourné twin law, than at the Albite and Carlsbad twin laws. Drawing the twin axis of the Albite twin, the size of the triangle of error is rarely less, than 3°. Frequently, the measure pole of the (010) intergrowth and cleavage plane does not fall into the triangle of error. If two twin complexes twinning Albite, Carlsbad and Roc-Tourné are perpendicular it characterizes the "Banat" intergrowth. If two complexes are neither parallel, nor perpendicular, and there are re-entering angle between them, it characterizes the Börzsöny and Visegrád twin laws. In spite of this conspicuous feature we can not determine the twin law without taking precise measurements. The angle is a function of the section and it can be delusive if one complex is twinning according to Albite, Carlsbad and Roc-Tourné, while the other according to Manebach, Acline, or Ala and Albite-Ala. In cases of the perpendicular and inclined intergrowth the zones with inclusions show, that they are twinning and not chance intergrowth. Figures 3 an 4 show two inclined intergrowth; the fourth is a Baveno twin, the third is a twinning according to a pinacoid being in the [001].