Vörös A. szerk.: Fragmenta Mineralogica Et Palaentologica 11. 1983. (Budapest, 1983)

Summing up the main pétrographieal features considered above, the following generalization seems to be justified; 1. Leucocratic amphibole and biotite andésite types (e.g. Bajdázó Hill, Pilisszentlélek) tend to contain relatively unfractured, inclusion-poor garnets while in the normal mesocratic types (hyperstenic amphibole andésites) garnets are strongly fractured, they contain many inclusions and they are often resorbed, or rounded, sometimes disintegrated. (Plate III, Figs. 1, 2). 2. The few inclusions present in garnet of the first type are mainly apatite and opaque grains (very probably ilmenite, see later), while in the second type, plagioclase predominates, amphibole and hyperstene may also be present. 3. The leucocratic varieties carry few phenocrysts and have very fine-grained matrix, in contrast mesocratic andésites contain many phenocrysts indicating intensive crystallization processes before the eruption. 4. In both the Visegrád and Börzsöny Mountains, besides garnetiferous andésites most other andésites that are mineralogically and chemically identical do not carry garnet. Garnets of Tóbércbánya (near the village of Szarvaskő, Western Bükk Mts) are quite different pétrographie ally from the preceding ones. As it was mentioned earlier, they occur in a leucocratic differenciated rock, a plagioclase granite that forms irregular shaped nests of several meters in the gabbro of Tóbércbánya. Neither the gabbro nor the diabase and the ultramafic rocks of this magmatic intrusion contain garnet, in contrast garnet is unusually abundant in the plagioclase granite: 6-8 larger grains (1-3 mm 0) and several smaller ones may be present within the area of a thin section! The plagioclase granite itself (abundant plagioclase + biotite + quartz and garnet) is a relatively fine-grained (aplitic) rock in contrast with the gabbro. Garnets are pink, without colour zoning and they never show idiomorphic outlines: the shape is irregular or rounded. As inclusions, they contain mostly small opaque grains, sometimes biotite especially in the more fractured border zone. CHEMISTRY OF THE GARNETS A greater number of electron microprobe analyses have been performed to obtain knowledge of the chemical composition, zoning of garnet in andesitic rocks and those of the plagioclase granite. A selected number of garnet analyses together with those of some inclusions of the garnet can be seen in Table 1 and Table 2. All the garnets analysed proved to be rich in almandine molecule. Garnets originating from andésites No significant differences in composition were found between megacrysts originating from the same source rock. Considering all measuring points in the garnets investigated, the minimum content of almandine should be taken at about 57% (Table 1). The second most important component may be pyrope (Csehvár), while it is grossular in the dark red and pink garnets of Királyrét. Spessartine remains < 5% in most cases. In addition, other differences in the composition may be studied in Table 1. The pink garnet of Királyrét has a higher average MnO content hence a greater percentage of spessartine than any other garnets originating from Hungarian andésites. The higher MnO content is counterbalanced mainly by smaller proportions of MgO. It should be assumed that these differences in their chemistry may be responsible for their lighter pink colour. Otherwise, differences in the average composition are not too important among the garnets of various localities. In contrast, important variability exists in the chemical homogeneity, and zoning pattern, e.g. the composition of the Csehvár garnets changes considerably relative to the others due to very important chemical zoning (Table 1, Fig. 3, 6, 7). In this case the strong compositional zoning is manifested in the reverse sense with the crystal becoming progressively and/or suddenly enriched in the pyrope component towards the margin (Fig. 3)