Szekessy Vilmos (szerk.): A Magyar Természettudományi Múzeum évkönyve 62. (Budapest 1970)

Szabó, I. ; Ravasz, Cs.: Investigation of the Middle Triassic volcanics of the Transdanubian Central Mountains, Hungary

less hematite and leucoxene occur. The unaltered part of the heavy minerals fraction is represented by apatite, zircon, rutile, garnet, and perovskite. Also the trachyte lava fragments, usually 300 to 400 tx in diameter, are rather sensibly cla\

7mineralized. being stained red-brown by limonite. On the basis of their abundance in samples T-709, -710, and -711, these can be determined as calcareous, crystallolithoclastic trachytic tuffs. The tuffaceous formations of exploratory shaft 3 of Aszófő show, practically, varying clay and CaC0

3 content. The volcanic detritus is of 50 tx average size, slightly sorted, slightly rounded. These characteristics as well as the mineralogical composition render the rock similar to the samples of borehole 5 at Pécsely (T-512, -514). In other words, the rock under consideration also represents a clay-mineralized trachytic tuff of varying crystallo-clastics content, enriched as a result of redeposition in situ. Predominant component of the clastic material is sanidine; besides, the amount of magmatic quartz and reoystallized volcanic glass fragments are considerable. Biotite is bleached, altered. As rock fragment, trachyte lava should be mentioned, calcarenite being subordinate. The rock is cemented partly by a netlace of sericite and montmorillonite, partly by streaks and minor patches of calcite. The pale yellow tuffs of medium hardness and slightly conchoidal fracture from the exploratory shaft of Örvényes represent crystallo-vitroclastic, altered tuffs, practically devoid of carbonate, being a term of transition between potashtrachitic tuff and rhyolitic tuff. Their crystal detritus is represented by unaltered sanidine (averaging 100 jx in diameter), quartz (120 u.), ragged, subordinate!}

7 altered biotite (120 u.), and accessory plagioclase. The clay mineral of illite-montmorillonite composition is represented by an interwoven netlace in narrow channels, globulites; incidentally, some zeolitization and secondary Si0

2 modification can be observed. Of the heavy minerals, some magnetite and limonite and needle-shaped apatite and, sporadically, some zircon are represented. The most typical sample of calcalkalic magmatité, occurring in a small amount in the area, derives from Nemesvámos. Macroscopically, it is a pale-yellow to greenisch-grey, unstratified, slightly altered, pumiceous rhyolitic tuff of medium hardness. The rock is constituted mainly by the fragments of the zeolitized volcanic glass, pumice (350-500 tx), oligoclase and quartz. Accessorily, some magnetite, apatite, and trachytic lithoclastics of fluidal texture are present. Oligoclase is limpid, albite- or Carlsbad-twinned, with an average grain diameter of 250 to 300 jx (max. 500 u.). Resorbed quartz is of similar size. Biotite is ragged, parity chloritized, 50 to 60 a in diameter. Among the minerals filling the original minute vesicles and channels of volcanic ash and pumice, zeolites are accompanied, in smaller amount, by montmorillonite, chalcedony, and opal. Carbonates are present in patches or independent rhombohedral crystals (sample N-2). Sample N-.1 is essentially more altered and in it both clay mineralization and carbonatization are more common than it is the case with the previous sample; however, volcanic glass fragments and altered feldspars can still be recognized well under the microscope. At Kádárta, the tuffs are connected with greenish-yellow, fine grained, cherty limestones of medium hardness, with apple-green patches and limonite dendrites. In this rock pumiceous rhyolitic tuff material is present as clastic component. The particles are sharp angular, of 500 to 1000 u. in diameter, the feldspars being represented by subidiomorphic, slightly elongated, platy oligoclase and andesine