Kaszab Zoltán (szerk.): A Magyar Természettudományi Múzeum évkönyve 72. (Budapest 1980)

Noske-Fazekas, G.: Statistical investigations of plagioclase twin laws in lavas erupted between the Danube and the Central Börzsöny Mountains (Hungary)

Fig. 1. Outline map of the area from which samples were collected. Key: 1 = pyroxene andésite, 2 = amphibole-pyroxene andésite, 3 = amphibole andésite, 4 = biotite andésite, 5 = oxyhornblende andésite, 6 = carbonatic amphibole andésite, 7 = dacite ed with the predominant constituent, the hyperstene, consequently, this group has had to be distinguished too. Most of the basic rock in the studied area is pyroxene andésite. Its colour is usually dark grey, though sometimes other colour shades also occur. This is a compact, very hard rock in which the Porphyrie constituents can hardly be distinguished from the groundmass when examined with an unaided eye. The rock is microhemicrystalline-porphyric in texture, but a pilotaxitic porphyric texture can also be observed in some of the samples. The groundmass constitutes nearly a half of the rock (Table 1), consisting of a fabric of mafic silicates, feldspar laths and partly recrystallized glass. Of the porphyric constituents, plagioclase feldspars are predominant, hyperstene is less abundan , while the other mafic silicates are much scarce (hornblende, biotite, augite). Silicate varieties resulting, from secondary alteration (zeolite, hydromica, etc.) are observable in small quantities. The rock variety in question is common from the southernmost tip of the Börzsöny (Ördöghegy at Nagymaros) up to its northernmost part (the Magas-Tax) (Fig. 1).