Szekessy Vilmos (szerk.): A Magyar Természettudományi Múzeum évkönyve 57. (Budapest 1965)
Csalogovits, I. J.: Geological and petrological conditions of the Szanda - Bercel area
2. Mt. Bercel a) Doleritic bytownite-andesite (roof andésite, quarry) Slight hydroandesitization of the rock can be noted macroscopically. Under the microscope the opaque accessories are larger than in the Szanda rock (0.25 mm). No microlites occur. The large porphyric interbeddings (2.5—4 mm) show intense zonality and contain many small, oriented magnetite inclusions. The ratio of minimum-maximum grain diameter of plagioclase porphyries here is 2.9: in the matrix it is 3.1. Both the degree of crystallization and the shape of the grains show a continuous transition toward matrix, the plagioclase generations are not sharply segregated from one another. The texture is doleritic. The opaque accessories in the matrix are large if compared to those of Szanda, and long, fibrous, opaque interbeddings are frequent. The feldspars are slightly montmorillomtized. The covering formation of Mt. Bercel is interwoven with hydrothermal dikes. In addition to doleritic bytownite-andesite that forms the main mass of the hill, several types of hvdroandesite can be found. The original material of these is similar, they only differ from one another in the degree of decomposition. b) Quarry „base andésite" This rock is very similar to the rock of the roof as concerns both composition and texture. 3. The rocks of the Istenhegy range. a) Augite-andesite (Istenhegy quarry). Macroscopically this rock is black, fresh. Opaque accessories, finely spread in the matrix, occur in large quantities. The glass content of the rock amounts to 15—20% at times, the plagioclase slats of an average size of 30 p. in the matrix of pilotaxitic texture are oriented along the fluxion lines. From among the porphyric components augite occurs in dominating quantities. The grains are rounded of and free from inclusions. Porphyric bytownite grains occur less often, are rounded and elliptical. A band of opaque inclusions of 30—60 \i thickness appears on the edges of the grains. Summing up the types enumerated in the foregoing : the Szanda rocks are characterized by large bytownite porphyroes with frequent, large augite inclusions in them; the Bercel rocks by doleritic texture and larger but less frequent opaque inclusions; the Istenhegy rocks by the presence of augite porphyries and a higher glass content. From the circumstance that the vulcanites of the area are similar in composition we may draw the conclusion that the formation of rock of varying mineral facies was the result of local changes in the rate of cooling and in the oxidation degree of the melt. It follows from the conditions of oxidation that, except for the Istenhegy rocks, the vulcanites are aphanitic, i. e. that the melt has not reached the oxidation-reduction potential necessary for augite formation by the time most of the rock solidified, therefore the bulk of mafitic accessories crystallized as magnetite — ilmenite. Contact investigations Andésite and the Chattian sandy clay series adjoining it along the contact line can be found in the artificial drift at level A 2 of the Szanda-Péterhegy quarry. The samples taken in the course of exploration were kept in a mine-wet condition in
