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

A dunabogdányi Csódi-hegy zeolitjai (Tóth Erzsébet, Weiszburg Tamás, Lovas György és Szakáll Sándor)

Topographia Mineralogica Hungáriáé Vol. VI. 141-159. Miskolc, 1999 A DUNABOGDÁNYI CSODI-HEGY ZEOLITJAI Zeolites of Csódi Hill (Dunabogdány, Visegrád Mts., Hungary) TÓTH Erzsébet, WEISZBURG Tamás, LOVAS György és SZAKÁLL Sándor Abstract: The Miocene dacite laccolith of Csódi Hill (Dunabogdány, Hungary) is interesting both from geological (Korpás, 1999) and petrographical-geochemical points of view (Harangi, 1999). Its zeolite assemblage occurring in hydrothermal cavities and cooling cracks has also been well known for a long time (Fig. 1, and see e.g. Reichert & Erdélyi, 1935). The paragenesis includes analcime, chabazite-Ca and stilbite-Ca accompanied by tubular aggregates of iron saponite and several generations of calcite (Fekete et al, 1999). This paper presents a mineralogical description of the cavity fdling zeolites. Analcime occurs mostly as 1-5 mm sized crystals ({211} combined with {100}, see Fig. 2). Crystals on the unaltered "bluish-grey" dacite are transparent (see Fig. 3 and Fig. X on the cover), while those on the weathered "yellowish-brown" rock are more or less cloudy (see Fig. IV on the cover). Chemical data and calculated formulae are given in Tables I—II (general formula is Nao.9[Alo.9-i.()SÍ2o-2.i06] • 0.9-1.3H2O). For density values see also Table II. Optical properties 2V0 20(2)°, cto 1.4860(3), ß0 1.4866(3), yD 1.4868(3) - and TEM SAED patterns (Fig. 4) suggest that analcime is orthorhombic ((Immm, /222 or Imm2); calculated unit cell parameters are as follows: a 13.737(3), b 13.747(6), c 13.705(1) Â (Table III). Chabazite-Ca appears both as rhombohedra (Figs. 5-7 and Fig. I on the cover) and as "phacolite" (see Figs. 8-11 and Figs. V, VIII and XI on the cover). The crystals vary widely in colour, transparency and size. Chemical data and calculated formulae are given in Tables IV-V (average formula is Cai.i_i.5Nao.3-!.3Ko.i-o.2[Ah.3.3.6Si8.5-8.7024] • 11.3-15.2H20), for density values see also Table V. Optical properties of phacolite are the same as those of the rhombohedral crystals, no 1.485(2) according to Reichert & Erdélyi (1934, 1935). The studied chabazite-Ca crystal is triclinic (P1 ), unit cell parameters - a 9.405(3), b 9.406(2), c 9.435(3) Â, a 94°28.2±1\ ß 93°48.2±1', y 94°39.0±1' - are compared to those calculated by Passaglia (1970) in Table VI. Stilbite-Ca occurs as tabular crystals and as sheaf-like (Figs. 12-14 and Fig. Ill on the cover) or radialglobular aggregates (Fig. XII on the cover). Analytical data and calculated formulae are given in Tables VII-VIII (average formula is Ca4.(M.2Nai.j-i.7Ko-o.2[Al9.7.9.8SÍ26.2072] • 29.0-33.5H2O), for density values see also Table VIII. The studied stilbite-Ca crystal is monoclinic (C2/m), unit cell parameters are: a 13.634(2), b 18.212(2), c 11.282(1) Á, ß 127°51±50' (Table IX). The XRPD pattern of spheroidal zeolite formerly identified as stellerite (Jánossy et al, 1987) shows strong evidence of monoclinity (Figs. 15-16), so this morphological variety is also stilbite-Ca (no presence of stellerite has been proved so far among the zeolites of Csódi Hill). Zeolites of Csódi Hill are products of hydrothermal activity. Hydrothermal cavities can be filled with zeolites only (1), zeolites and different generations of calcite (2) or zeolites and iron saponite (3). Iron saponite often occurs as inclusion in zeolites (Figs. V-VI, VIII and XI on the cover). Several zeolite generations are assumed. The first one - small, transparent analcime and chabazite-Ca crystals - is widespread in the neighbouring area as well (Visegrád Mts., Southern Börzsöny Mts.; Table X). The second generation - zeolites showing great variability both in form and colour - is characteristic only for Csódi Hill. The succession trend proposed by Reichert & Erdélyi (1935), i.e. chabazite-Ca (incl. phacolite) - analcime - stilbite-Ca, was proved with strongly overlapping crystallisation periods. Chabazite-Ca can be both older and younger than analcime, but sheaf-like stilbite-Ca is always the youngest zeolite. Calcite formed during the whole zeolite crystallisation period, while iron saponite is connected only to the late stage of crystallisation. Stable isotope data of calcite (Fekete et al, 1999) and analcime (Demény et al, 1997) also confirm that these minerals formed during the same crystallisation period. Calcite and iron saponite accompanying zeolites never appear in the same cavity, which may be a result of completely different genetic circumstances.