Tufit z Barczy koło Zagnańska

Abstract

TUFFITE FROM BARCZA MOUNTAIN NEAR ZAGNAŃSK (ŚWIĘTY KRZYŻ MOUNTAINS)

The occurrence of tuffite·amidst Lower Devonian (Emsian) sandstones of Barcza Mountain has been observed for the first time by J. Czarnocki (1937). The tuffite appears here in three different horizons in the shape of fairly thin beds of green colour (30 to 70 cm. thick).

In Table 1 are represented (in weight %) the results of a mechanical analysis, of planimetric measurements and of quantities of components of the investigated tuffite. This tuffite shows a varying texture: crystallolithoclastic in the coarser grain variety·and crystalloclastic in the finegrained, schistaceous variety. Among the components, celadonite predominates; furthermore, there are: quartz in small bipyramidal firagments and crystals, fresh potassium feldspar optically positive (2V° =26-40°), kaolinized feldspar, fragments of felsites and sedimentary rocks. The glass is completely devitrified, and scarcely relics of its contours are preserved (Fig. 3).

The chemical character of the tuffite and its mineral composition (both normative and modal), have been given in Table 2 of the Polish text.

For purposes of comparison the author has presented, in Table 3 of the Polish text, next to the chemical composition of the Barcza tuffite 1) (in weight %), likewise the analyses of both the tuff from Filipowice (Cracow Region, 2) and the tuffite from Bocianówka (Wolhynia, 3) which both chemically resemble the Barcza tuffite.

It is the author's opinion that the Barcza tuffite is connected with an extrusion of acid rocks of porphyry type. The pyrogenic material has undergone relatively short eoIian transportation. Subsequently, the tuffite underwent alteration due to hydrothermal processes owing to which there was produced celadonite and quartz with inclusions of celadonite, of other solid bodies and of fluids and gases.

It seems probable that some plates of idiomorphic feldspar with sanidine features have also been produced by hydrothermal alterations.