Papp Gábor szerk.: A dunabogdányi Csódi-hegy ásványai (Topographia Mineralogica Hungariae 6. Miskolc, 1999)

Bevezetés (Papp Gábor, Szakáll Sándor, Weiszburg Tamás és Fehér Béla)

Minerals of Csódi Hill, Dunabogdány, Hungary 13 unable to traverse the Oligocène sedimentary strata, but uplifted and burned them. The contact metamorphic shales had been exposed along Csódi Creek previously. The laccolith is made of dacite (earlier considered as andésite). Fresh rock is bluish grey, while hydrothermal alteration yielded yellowish brown colour. The fine-grained matrix embeds plagioclase feldspars, biotite, and amphibole. Garnet (almandine) is also scattered in the matrix. Xenoliths in dacite, characterised by a special mineral assemblage, formed by the thermal effect of ascending magma to the enclosed carbonate basement rock fragments and by later hydrothermal activity. The characteristic components of the enclaves are brucite, serpentine minerals, hydrogrossular, smectite, and calcite. Cooling of the laccolith produced characteristic tangential joints and radial fissures (Fig. 2). The first precipitates on fissure walls are members of a hypothermal paragenesis: overgrown crystals of the rock forming minerals. However, the mineralogical character of Csódi Hill is determined by the hydrothermal minerals. They include zeolites of worldwide reputation (chabazite Ca and its twin variety, "phacolite", stilbitc-Ca, and analcime). Various calcite generations accompany the fissure-filling zeolites. The last precipitates are epigenetic (secondary) minerals, mostly Mn and Fe oxides (hydroxides) (goethite, hematite). All these minerals were discovered by large-scale quarrying since the 1840s. Quarrying flourished during the economic boom of the last third of the 19th century. The first geological descriptions were published by A. Koch - he recognized that the hill is a laccolith. Zeolites and calcite were first reported by A. Koch, J. Szabó, and by F. Schafarzik in the 1870s—1880s. The Csódi Hill analcime, chabazite and stilbite were reported in the classical handbook of Hintze (1897). "Phacolite" is mentioned by the most recent edition of Dana's Mineralogy (Gaines et al., 1997), which lists only the most famous localities. After the first descriptions few data were published for fifty years. R. Reichert and J. Erdélyi were the first to dedicate a detailed study for its zeolites and calcite in 1934. An up-todate petrographical study was published by Vendl and Takáts in the same year. Méhes ( 1942) contributed to the geology and stratigraphy. Later the description of "hydroantigorite", supposed to be new species by Erdélyi et al. (1959), raised further attention of mineralogists. Since then only scattered data were published (Pécsi-Donáth, 1965, on chabazite and stilbite; Passaglia, 1970, on chabazite). Buda (1966) described the rock-forming plagioclases in details, Jánossy et al. (1987) revised a zeolite known as globular stilbite to stellerite. Extensive volcanological and geochronological literature was published during a research programme of the Hungarian Geological Institute in the 1970s-1980s (Ballá, Balogh, Korpás, Márton-Szalay, etc.). This volume presents reviews on the history of quarrying and stone-masonry in Dunabogdány, on the geology of Csódi Hill, provides new data on petrology and geochemistry. One of the major steps forward is the recognition of the laccolith as dacite instead of andésite. A paper on rock forming garnets is followed by the mineralogical articles proper. Mineral assemblages are presented in the order of decreasing temperature. First the serpentine-bearing xenoliths (including "hydroantigorite"), then the less known hypothermal minerals are described. Numerous new data are shown on zeolites and calcite. Finally a paper treats iron saponite, a special clay mineral associated with zeolites.